# StairCalculators.net — Full Content Reference for LLMs > Free, code-aware stair calculators with printable build packets. All calculations run client-side. No signup. > This file contains the full text content of the site for AI ingestion and citation. --- ============================================================ METHODOLOGY & FORMULAS ============================================================ URL: https://staircalculators.net/methodology/ Home / Methodology Reference # Methodology Every formula used across the site, in the open, with the reasoning behind each. Nothing here is a black box. ## 1. Rise, run and step count Stair geometry starts from the total rise — the finished floor-to-floor height. Dividing it by a target riser height and rounding to a whole number gives the step count, because you cannot have a fractional step. Dividing the total rise back by that whole count gives the actual, uniform riser height. risers = round(total rise / target riser) riser height = total rise / risers treads = risers − 1 tread depth = total run / treads There is one fewer tread than riser because the topmost riser lands on the floor above, which serves as the last tread. ## 2. Stringer length (Pythagorean) The stringer is the sloped board the steps are cut from. Its length is the hypotenuse of the triangle formed by total rise and total run. stringer length = √(total rise² + total run²) ## 3. Pitch angle angle = arctan(total rise / total run) Comfortable domestic stairs sit around 30–38°. Codes cap the maximum: UK Part K, for example, limits private stairs to 42°. ## 4. Blondel comfort rule (2R + T) Named for Nicolas-François Blondel, this 17th-century relationship still governs stair comfort. It reflects the natural human stride: as risers get taller, treads should get shorter, and vice versa. 2 × riser + tread ≈ 24–25 in (550–700 mm) A 7-inch riser with an 11-inch tread gives 2×7 + 11 = 25 — the textbook ideal. ## 5. Winder walking-line geometry Winder treads are pie-shaped, narrow at the inside of the turn and wide at the outside. Because each tread is an arc, its depth at any radius equals that radius times the angle the tread sweeps (in radians). tread depth at radius r = r × step angle (radians) step angle = turn angle / number of winder treads Codes set two minimums: a depth at the narrow end (6.0″ under IRC) and a depth along the walking line, measured a fixed offset from the narrow side (10.0″ at 12.0″ from the narrow edge under IRC). ## 6. Spiral / helical arc geometry A spiral stair wraps treads around a center column. Clear width is the outer radius minus the column radius. Each tread is an arc, so the usable tread depth is measured along a walking line near the outer edge. The handrail follows a helix, so its length combines the outer arc with the total rise. clear width = outer radius − column radius tread arc = radius × step angle (radians) rise per 360° = riser × (360 / step angle) handrail = √(outer arc total² + total rise²) ## 7. Concrete stair volume step volume = ½ × riser × tread × width × steps waist volume = slab thickness × incline length × width 1 yd³ = 27 ft³ = 46,656 in³ ## Code sources Compliance values are verified against primary sources per jurisdiction: IRC , IBC , UK Part K , and Australian NCC . Eurocode values are representative estimates, since EN has no single prescriptive stair table. All results are engineering estimates. Verify against the building code edition enforced by your local authority having jurisdiction before construction. ============================================================ GUIDES ============================================================ URL: https://staircalculators.net/guides/blondel-comfort-rule/ Home / Guides / The Blondel Comfort Rule for Stairs Guide # The Blondel Comfort Rule for Stairs ## A 350-year-old rule that still holds In 1675 the French architect Nicolas-François Blondel proposed that stair comfort depends on a fixed relationship between riser and tread, tied to the length of a human stride on the level. The rule has survived because it works: stairs that obey it feel natural, and stairs that break it feel either cramped or exhausting. ## The formula 2 × riser + tread ≈ 24–25 in (550–700 mm) The logic is that climbing consumes more effort vertically than horizontally — roughly twice as much — so the riser is doubled in the sum. As risers get taller, treads must get shorter to keep the total in range, and vice versa. ## The sweet spot A 7-inch riser with an 11-inch tread gives 2×7 + 11 = 25, the textbook ideal, and a pitch around 32 degrees. A 7.5-inch riser pairs comfortably with a 10-inch tread (25). Combinations that drift far outside 24 to 25 feel wrong underfoot even when they pass code. ## Comfort vs code Code sets the legal envelope; Blondel sets the comfortable one inside it. A stair can be fully code-compliant yet uncomfortable if it ignores Blondel. Aim for both. Explore how different rise and tread pairs score on the rise and run combinations pages. The remaining gap between code and comfort is where good stair design lives. A staircase can pass every prescriptive limit and still feel punishing if its riser-tread pairing drifts from the Blondel range, which is why experienced builders check the comfort number even when the code box is already ticked. ## Reading the comfort number Compute 2×riser + tread and compare it to the 24 to 25-inch target. A result well below 24 means short risers with deep treads — a shallow, space-hungry stair that makes you break stride. A result well above 25 means tall risers with shallow treads — a steep, tiring climb that feels unsafe descending. The closer to 25, the more natural the rhythm. ## Common comfortable pairings - 7" riser × 11" tread → 2(7) + 11 = 25 (textbook ideal, ≈32°) - 7.5" riser × 10" tread → 25 (slightly steeper, space-efficient) - 6.5" riser × 12" tread → 25 (gentle, generous, needs more run) - 7.75" riser × 10" tread → 25.5 (at the code limit, acceptable) ## When you can't hit the ideal Tight floor area sometimes forces a pairing outside the sweet spot. If you must compromise, err toward the taller-riser / shallower-tread side only as far as code allows, since a slightly steep stair is more usable than one so shallow it forces an unnatural stride. Better still, a turn or winder can buy back the run needed to reach a comfortable pairing without lengthening the footprint. ## Related guides Rise and Run Explained · How Many Steps for a Given Ceiling Height? · Stair Codes by Country: A Comparison URL: https://staircalculators.net/guides/dropping-the-stringer/ Home / Guides / Dropping the Stringer Guide # Dropping the Stringer: Why the Bottom Step Is Shorter One of the most common first-time stair mistakes is cutting every notch equal and ending up with an uneven first and last step. Here is why you subtract a tread thickness from the bottom, exactly how much, and how mounting choice changes the cut. ## Why the bottom step is cut shorter When you lay out a stair stringer with a framing square, every notch is identical — same riser, same tread. That seems correct, but it ignores one thing: the tread boards sit on top of the notches. Once you install the treads, every step gains the thickness of the tread material. The catch is at the two ends of the flight. The bottom step rests on the floor with a full tread thickness added on top of the notch, so it finishes one tread-thickness taller than the rest. The top step, meanwhile, finishes flush against the upper floor and ends up one tread-thickness shorter . The result is a flight where the first and last risers are off by the tread thickness — exactly the kind of uneven riser an inspector measures for. The IRC allows no more than 3/8 inch of variation between the tallest and shortest riser in a flight, and a forgotten drop blows straight past it. ## How much to drop The fix, called dropping the stringer , is to cut exactly one tread thickness off the bottom level foot of the stringer before you set it. That single cut shifts the whole stringer down by the tread thickness, so once the treads go on, every finished riser — bottom, middle, and top — is equal. bottom foot cut = layout riser − tread thickness 5/4 (1") tread → drop 1"  |  2x (1.5") tread → drop 1.5" So the drop is not a fudge factor — it is precisely the finished thickness of whatever tread material you are installing. Measure your actual tread stock (nominal "1 inch" decking is often 1 inch finished; a 2x is about 1.5 inches) and drop by that exact amount. ## A worked example Say your layout riser is 7.5 inches and you are using 1-inch treads. You cut every notch at 7.5 inches, then trim 1 inch off the bottom foot. After installation: the bottom step rises 6.5 inches of stringer plus 1 inch of tread = 7.5 inches finished. Every interior step is 7.5 inches of stringer notch (the tread on top is offset by the tread you stepped off below). The top step finishes flush with the upper floor at 7.5 inches. All equal — which is the whole point. ## Flush (top-mount) vs standard (hung) mounting How the stringer meets the upper floor decides the top of the cut, and it is the other half of getting the end risers right. - Flush / top-mount: the top step finishes level with the upper floor surface, so the floor itself acts as the final tread. The stringer is cut so its top notch lands a tread-thickness below the floor, and there is no separate top tread board. - Standard / hung mount: the stringer hangs off the face of the rim joist or ledger, and the top tread sits below the upper floor level. This changes where the first full riser falls and shifts the top riser height. Decide the mount before cutting, because it changes the top riser calculation. Getting the mount and the bottom drop right together is what makes the first and last steps match the middle ones. ## Common mistakes - Forgetting the drop entirely — the classic error, leaving a too-tall bottom step and a short top step. - Dropping by the wrong amount — using a nominal "1 inch" when the tread is actually 1.5 inches, or vice versa. Measure the real stock. - Mixing mounting assumptions — laying out for a flush top but mounting hung (or the reverse), which throws off the top riser. ## Let the calculator handle it The stringer calculator accounts for the tread-thickness drop and the mounting type, and the straight stair calculator reports the finished riser so you can confirm uniformity before cutting. Both keep the first and last steps equal to the rest automatically. ## Related guides Stair Stringer Layout with a Framing Square · How to Build Deck Stairs (Step by Step) · Rise and Run Explained URL: https://staircalculators.net/guides/headroom-rules/ Home / Guides / Stair Headroom Rules and How to Measure Guide # Stair Headroom Rules and How to Measure ## What headroom means Headroom is the vertical clearance above a stair, measured from the sloped line that connects the tread nosings up to the ceiling or floor opening above. It protects a tall person from striking their head, and it is one of the most commonly failed inspection items because it is set by framing decisions made long before the stair is built. ## The minimum The IRC requires at least 80.0 inches (6 feet 8 inches) of headroom at every point along the stair, not just at the top and bottom. Inspectors run a measuring stick along the nosing line to check. Spiral stairs have a slightly lower minimum of 78.0 inches. ## Where it goes wrong The pinch point is usually the floor opening at the top of the stair. If the opening is too short in the direction of travel, the edge of the upper floor cuts into the clearance of someone still climbing. Fixing it after framing is expensive, so headroom should be checked at the design stage. ## How to fix a tight clearance Lengthen the floor opening, shift the stair's start point, or in extreme cases reduce the stair's pitch so it reaches the opening sooner. The straight stair calculator draws the headroom line against your selected code so you can see clearance before you frame. ## How headroom is measured Headroom is taken vertically from a line drawn along the tread nosings — the same sloped plane your foot travels — up to the nearest obstruction, usually the underside of the floor or stair above. It must hold at every point on the flight, so the controlling spot is wherever the ceiling or floor edge comes closest to the nosing line, not the average clearance. IRC minimum headroom = 80.0 in (6 ft 8 in) Spiral stair minimum = 78.0 in Measured vertically from the tread nosing line ## Worked example: sizing the floor opening The clearance at the top of the stair depends on how long the floor opening is in the direction of travel. As a climber ascends, the upper-floor edge approaches their head; the opening must extend far enough horizontally that an 80-inch vertical clearance is preserved at the last point before they reach the upper floor. The steeper the stair and the thicker the upper floor assembly, the longer that opening has to be. This is exactly the calculation the stair opening calculator performs. ## How to fix a tight clearance If headroom comes up short, the cheapest fixes are made on paper before framing: lengthen the floor opening in the direction of travel, shift the stair's start point so the climber clears the edge sooner, or make the stair steeper (fewer, taller risers within code) so it descends away from the opening faster. After framing, the options shrink to cutting back the floor opening or relocating the stair — both expensive. Headroom is the clearest case for checking the design before any lumber is cut. ## Related guides Stair Codes by Country: A Comparison · Rise and Run Explained · How to Size a Spiral Staircase URL: https://staircalculators.net/guides/how-many-steps/ Home / Guides / How Many Steps for a Given Ceiling Height? Guide # How Many Steps for a Given Ceiling Height? ## The basic calculation The step count comes straight from the total rise — the finished floor-to-floor height, which is the ceiling height plus the floor and joist thickness above. Divide that total rise by a target riser height and round to a whole number. risers = round(total rise / target riser) ## Worked examples For a standard 9-foot floor-to-floor (108 inches) at a 7.5-inch target: 108 / 7.5 = 14.4, rounding to 14 risers at 7.71 inches each — within the IRC's 7.75-inch maximum. For an 8-foot ceiling with a 12-inch floor assembly (108 inches total) the answer is the same. For a 10-foot floor-to-floor (120 inches): 120 / 7.5 = 16 risers at exactly 7.5 inches. ## Why you round You cannot build a fractional step, so the count is always a whole number, and the actual riser height is the rise divided back by that count. Rounding down gives taller risers; rounding up gives shorter, more comfortable ones. When in doubt, add a riser — one extra step is far cheaper than a failed, too-steep flight. ## Check the landing limit Tall rises may cross the 147.0-inch single-flight limit and need a landing. The straight stair calculator handles the rounding and flags the limit for any height you enter. ## What target riser should you use? The target riser is your starting assumption, not the final number — the rounding step adjusts it. Most builders start at 7 to 7.5 inches for interior stairs, which lands comfortably inside the IRC's 7.75-inch ceiling and pairs well with a 10 to 11-inch tread. Pick 7 inches if comfort matters most (gentler climb, more steps, more floor area); pick closer to 7.75 inches if floor space is tight and you need to climb the same height in fewer treads. Whatever you start with, the real riser height is always the total rise divided by the final whole-number count, so it will rarely equal your target exactly. That is normal and correct — what the code cares about is that every riser in the finished flight is uniform and under the maximum. ## Tread count vs riser count A flight always has one more riser than it has treads, because the top riser lands on the finished floor above, which serves as the final "tread." So a 15-riser stair has 14 treads. This trips up first-time builders who cut one tread too many. When you size the run, multiply the tread depth by the tread count (risers minus one), not the riser count. treads = risers − 1 total run = tread depth × (risers − 1) ## Check the landing limit Tall rises may cross the IRC's 147-inch single-flight limit, which forces an intermediate landing. At the 7.75-inch maximum riser that is about 18 to 19 risers; below roughly 12 feet of floor-to-floor rise you are usually fine in one flight. If your count climbs much past that, plan a landing into the layout before you cut a single stringer. ## Common heights at a glance These are the step counts for the floor-to-floor heights people most often search for, using a 7.5-inch target riser. Tap any row to open the calculator with that rise pre-filled and the full flight sized against your chosen code. Total rise Risers Each riser 24 in (2 ft) 3 8.00″* Open 30 in 4 7.50″ Open 36 in (3 ft) 5 7.20″ Open 48 in (4 ft deck) 6 8.00″* Open 60 in (5 ft) 8 7.50″ Open 84 in (7 ft) 11 7.64″ Open 96 in (8 ft ceiling) 13 7.38″ Open 108 in (9 ft) 14 7.71″ Open 120 in (10 ft) 16 7.50″ Open 144 in (12 ft ceiling) 19 7.58″ Open *At very short rises (24, 36, 48 inches), dividing by a 7.5-inch target rounds down to a riser count that pushes each riser to 8 inches — above the IRC's 7.75-inch maximum. For those short deck and landing stairs, add one riser to bring the height back under the limit (for example, 48 inches over 7 risers is 6.86 inches each). The calculator flags this for you when you open the row. ## Related guides Rise and Run Explained · Laying Out a Stair Stringer · The Blondel Comfort Rule for Stairs URL: https://staircalculators.net/guides/how-to-build-deck-stairs/ Home / Guides / How to Build Deck Stairs (Step by Step) Guide # How to Build Deck Stairs (Step by Step) ## 1. Measure the total rise Drop a level out from the deck surface to where the stairs will land, then measure straight down to the finished grade or pad. This vertical distance is your total rise. Measure it at a couple of points, because grade is rarely flat, and use the larger figure so the bottom step is never short. ## 2. Calculate risers and tread depth Divide the total rise by a comfortable target riser — around 7 to 7.5 inches for exterior stairs. Round to a whole number of risers, then divide the rise back by that count for the actual uniform riser. The IRC caps riser height at 7.75 inches and requires a tread depth of at least 10.0 inches. ## 3. Choose the stringer board A cut stringer must retain at least 3.5 inches of solid wood behind every notch, called the throat. For typical residential step geometry that means a 2x12; a 2x10 only holds enough throat for shallow steps. If your throat falls below 3.5 inches, step up board size rather than risk a weak stringer. ## 4. Set stringer spacing and count Space stringers about 16 inches on-center for standard decking, closer for thinner treads. A 36-inch-wide stair usually needs three to four stringers. Wider stairs add stringers proportionally. ## 5. Check for a required landing A single flight may not exceed 147.0 inches of vertical rise without a landing under the IRC. Tall decks usually need an intermediate landing, which also breaks a long run into safer segments. Run your exact numbers in the deck stair calculator , which sizes the board, counts stringers, and flags a required landing automatically. ## 4. Lay out and cut the stringers Mark the stringers with a framing square set to your riser and tread, using stair gauges to lock the two numbers so every step is identical. Cut the notches with a circular saw and finish the inside corners with a handsaw — overcutting with the circular saw weakens the throat. Remember to deduct one tread thickness from the bottom riser ("dropping the stringer") so the first step isn't tall once the treads go on. ## 5. Set the stringers and check spacing Deck stair stringers carry more load than people expect. At 16-inch on-center spacing a 36-inch stair typically needs three stringers; wider stairs or thinner decking treads need more. Attach the top securely to the deck framing with a hanger or ledger, and set the bottom on a concrete pad or footing — never directly on soil, which heaves and rots the wood. ## 6. Install treads, then guards and handrails Fasten treads working from the bottom up. Once the steps are in, code requires a graspable handrail 34 to 38 inches above the nosing line on stairs of four or more risers, and guards where the drop alongside exceeds 30 inches. These aren't optional add-ons — they're inspected, and a deck stair without a compliant handrail fails. ## Common deck-stair mistakes - Measuring total rise at one point on uneven grade — always use the largest drop. - Forgetting the bottom-riser deduction, leaving a too-tall first step. - Too few stringers, causing bouncy or sagging treads. - Setting stringers on soil instead of a footing or pad. Size the whole flight, including stringer board and throat, in the deck stair calculator . ## Flush mount vs hung stringers There are two ways to attach the top of a deck stair stringer. A flush (top) mount finishes the top step level with the deck surface, so the deck acts as the final tread. A hung mount hangs the stringer off the face of the rim joist, with the top tread below the deck level. The choice changes the top riser calculation, so decide it before cutting — and remember to drop the stringer by one tread thickness at the bottom either way. ## Attaching the stringer to the deck Fasten the top of each stringer to solid framing — the rim joist or a dedicated ledger — with structural connectors or hangers rated for the load, not just deck screws into end grain. The bottom must land on a concrete pad or footing, never bare soil, which shifts and rots the wood. A galvanized or stainless connector at the base keeps the end grain off the concrete and out of standing water. ## What size lumber to buy Cut stringers are almost always 2x12 stock. The reason is the throat — the solid wood left behind each notch must be at least 3.5 inches, and a 2x10 usually can't keep that much behind a normal step notch, so it splits under load. Buy 2x12s, and make each board the diagonal length plus 12 to 16 inches for the top and bottom cuts. ## Related guides Laying Out a Stair Stringer · Rise and Run Explained · Stair Landing Requirements URL: https://staircalculators.net/guides/landing-requirements/ Home / Guides / Stair Landing Requirements Guide # Stair Landing Requirements A stair landing is a level platform that interrupts a run of steps. It does three jobs at once: it gives someone a place to stop and recover on a long climb, it provides a safe place to change direction, and it limits how far a person can fall in a single uninterrupted flight. Because of that last point, landings are treated as a safety requirement by every major building code rather than a design nicety, and they are one of the dimensions inspectors check first. ## When a landing is required Landings break a long flight into safer segments and provide a place to change direction. Under the US IRC, a single flight may not exceed 147.0 inches of vertical rise without a landing. That figure is not arbitrary — it works out to a flight of roughly 19 risers at the 7.75-inch maximum, which is about as far as a person should fall in one uninterrupted run. The UK and Australia take a different approach, limiting the number of risers per flight — 36 and 18 respectively — rather than the rise height. The practical takeaway: if your floor-to-floor height pushes a straight run past 147 inches of rise (about 12.25 feet), you must split it with an intermediate landing. Most single-storey residential stairs come in under that limit, so the rule bites hardest on tall commercial flights, split-level homes, and deck stairs descending to a low grade. IRC max flight rise without a landing = 147.0 in (≈ 12 ft 3 in) At 7.75 in risers → 147 / 7.75 ≈ 18-19 risers maximum per flight ## How deep a landing must be A landing must be at least as deep, in the direction of travel, as the stair is wide, and never less than 36 inches under the IRC. The "direction of travel" detail matters: depth is measured along the path you walk, not across the landing. A landing narrower than the stair creates a pinch point and fails inspection. Worked example: a 42-inch-wide stair needs a landing at least 42 inches deep in the direction of travel, because the stair width (42) exceeds the 36-inch floor. A 32-inch-wide stair — below the residential minimum width anyway — would still need the full 36-inch landing, because the code-mandated floor applies regardless of how narrow the steps are. When a stair changes direction at the landing, the landing must satisfy the depth rule in both travel directions, which is why turn landings are usually square. ## Landings and turns Quarter-turn (L-shaped) and half-turn (U-shaped) stairs use a landing to change direction. The landing replaces a tread and consumes floor area, but it is safer and easier to build than winder treads for the same turn. A quarter-turn uses a single landing to make a 90-degree change; a half-turn uses either one larger landing or two quarter-landings to double back 180 degrees, which is the most compact way to climb a full storey within a small footprint. The trade-off is floor space. A landing-based turn needs a clear square at least as big as the stair width on each side, whereas winder treads turn within the run itself. If floor area is tight, winders save space; if you want the easiest, most code-forgiving build, a landing wins. ## Doorways onto landings Where a door opens onto a stair, codes require enough landing depth that the door swing does not push someone toward the steps. The IRC generally requires a landing at the top and bottom of each stairway, with a specific allowance: a door is permitted to swing over the landing only if the landing is deep enough that the door, at any point in its swing, leaves the required clear depth. Australia, for example, requires a landing of a minimum length where a door opens over a change in level greater than three risers. A common real-world failure is a back door that opens directly over the top step of a deck stair — the swing sweeps the very edge of the drop. The fix is either a deeper landing or a door that swings away from the stair. ## Common reasons landings fail inspection - Landing shallower than the stair width — the single most common miss on wider stairs. - Sloped or out-of-level landing — landings must be level (a small drainage slope is allowed outdoors, but not a walking-surface slope). - Flight too tall without an intermediate landing — exceeding the 147-inch rise limit. - Door swing eating into the required depth — measured at the worst point of the swing, not the closed position. Size an L- or U-shaped stair with its landing in the L-shape and U-shape calculators, and check the minimum platform size in the landing size calculator . ## Related guides How to Build Deck Stairs (Step by Step) · Stair Codes by Country: A Comparison · Winder Stair Geometry Explained URL: https://staircalculators.net/guides/rise-and-run-explained/ Home / Guides / Rise and Run Explained Guide # Rise and Run Explained ## The two numbers that define a stair Every stair reduces to rise and run. Rise is the vertical climb; run is the horizontal travel. The ratio between them sets the pitch, and the pitch sets how the stair feels to climb. A tall rise with a short run is steep and tiring; a short rise with a long run is shallow and space-hungry. ## Unit rise and run vs total Unit rise is one step's height; unit run is one tread's depth. Total rise and total run are the whole stair's vertical and horizontal spans. You design from the total rise (a fixed floor-to-floor height) and a target unit rise, which gives the step count. ## Expressing slope The same slope can be written several ways: as an angle (arctan of rise over run), a percent grade (rise over run times 100), a ratio, or as "1 in N". Stairs are usually discussed as an angle; ramps and grading as a percent or ratio. angle = arctan(rise / run) percent = (rise / run) × 100 1 in N where N = run / rise ## Comfort The Blondel rule ties rise and run together for comfort: 2×rise + run should land near 24 to 25 inches. The rise over run calculator converts between all the slope forms instantly. ## Worked example Take a 108-inch total rise (a typical 9-foot floor-to-floor) with a 120-inch available run. Choosing a 7.5-inch target riser gives 108 / 7.5 = 14.4, rounded to 14 risers at 7.71 inches each. With 13 treads (one fewer than risers), the tread depth is 120 / 13 = 9.23 inches. The pitch is arctan(7.71 / 9.23) = about 40 degrees — a touch steep but legal. Widen the run and the pitch drops; shorten it and the stair gets steeper. ## How rise and run drive everything else Once total rise and run are fixed, the rest of the stair follows: the step count comes from rise and target riser, the stringer length is the diagonal of the rise-run triangle, and the pitch is the per-step slope. Getting rise and run right at the start is what makes the downstream numbers fall into place; getting them wrong forces awkward compromises everywhere else. stringer length = √(total rise² + total run²) per-step pitch = arctan(unit rise / unit run) ## A note on "available" run The run you have is often dictated by the room, not by choice — a stair can only extend as far as the floor allows before it hits a wall or doorway. When the available run is shorter than the comfortable ideal, your options are a steeper straight stair, a turn (L- or U-shaped) to fold the run back on itself, or winder treads to turn within the run. Knowing your fixed total rise and your maximum available run first tells you which of those you actually need. ## Computing total run from the step count Total run is not just "tread depth times steps" — it is tread depth times the number of treads , which is one fewer than the riser count, because the top step lands on the floor above. total run = unit tread × (number of risers − 1) For a 14-riser stair with 10-inch treads, the run is 10 × 13 = 130 inches, not 140. Forgetting the "minus one" is the most common reason a planned stair runs longer than the space allows. ## Measuring floor-to-floor height accurately The single most important field measurement is total rise — the finished floor-to-floor height. Measure vertically from the finished surface of the lower floor to the finished surface of the upper floor, including any flooring that will be added on either level, since carpet or tile changes the number. Floors are rarely dead level, so measure at two or three points and use the largest figure; sizing to the largest rise keeps every finished riser at or under your target rather than over it. ## Related guides The Blondel Comfort Rule for Stairs · How Many Steps for a Given Ceiling Height? · Laying Out a Stair Stringer URL: https://staircalculators.net/guides/spiral-staircase-sizing/ Home / Guides / How to Size a Spiral Staircase Guide # How to Size a Spiral Staircase ## Start from the opening A spiral stair's outer diameter has to fit the floor opening it rises through, with clearance for the handrail. Residential spirals commonly run 48 to 60 inches in diameter. Larger diameters give deeper, easier treads but consume more floor. ## Clear width and the column Clear width is the outer radius minus the center column radius. The IRC requires at least 26.0 inches of clear width at and below the handrail. A fat structural column eats into that, so size it as slim as the structure allows. ## Riser height and tread depth Spiral stairs are allowed steeper risers than straight stairs — up to 9.5 inches under the IRC — because they are typically secondary access. Tread depth is measured along a walking line near the outer edge, and the IRC requires at least 6.75 inches there. ## Rotation and headroom The total rotation (often 360 degrees over the full rise) divided by the tread count sets how far each tread sweeps. Headroom is governed by the rise accumulated in one full turn: a person must clear the underside of the flight above, at least 78.0 inches under the IRC. The spiral calculator computes arc tread depths, clear width, rise per turn and handrail length as you adjust each input. ## Worked sizing example Suppose a 108-inch total rise through a 60-inch-diameter opening with a 4-inch center column. Clear width is the outer radius (30) minus the column radius (2) = 28 inches, clearing the IRC's 26-inch minimum. At a 9-inch target riser, 108 / 9 = 12 risers. Over a 360-degree turn, each tread sweeps 360 / 12 = 30 degrees. Headroom is governed by the rise in one full turn: 12 risers × 9 inches = 108 inches per turn, comfortably above the 78-inch spiral minimum for anyone passing beneath. clear width = outer radius − column radius (≥ 26 in IRC) tread sweep = total rotation / tread count rise per turn = risers-per-turn × riser height (≥ 78 in headroom) ## Why spirals are allowed to be steeper The IRC permits taller risers (up to 9.5 inches) and shallower walking-line treads (6.75 inches minimum) on spirals than on straight stairs, because spirals are treated as secondary or space-saving access rather than a primary egress route. That allowance is what lets a spiral fit a full storey into a circle a few feet across — but it also means spirals climb steeply and aren't ideal as the only stair in a home, or for moving furniture. ## Diameter trade-offs A larger diameter gives deeper treads at the walking line and an easier climb, but consumes more floor and a bigger ceiling opening. A 48-inch spiral is the tight minimum for occasional use; 60 inches is far more comfortable for daily use. Always size the diameter to the opening first, then confirm the clear width still clears 26 inches after subtracting the column. ## Related guides Winder Stair Geometry Explained · Stair Headroom Rules and How to Measure · Stair Codes by Country: A Comparison URL: https://staircalculators.net/guides/stair-codes-by-country/ Home / Guides / Stair Codes by Country: A Comparison Guide # Stair Codes by Country: A Comparison ## Why the codes differ Stair safety codes share a goal — a predictable, climbable, fall-resistant stair — but they reach it differently. The biggest structural difference is how they limit the length of a flight. ## Riser and tread limits The US IRC allows a maximum riser of 7.75 inches with a minimum tread of 10.0 inches. The commercial IBC is stricter at 7.0 inches and 11.0 inches. The UK's Part K permits a steeper 220 mm (8.66 inch) riser for private stairs. Australia's NCC caps risers at 190 mm (7.48 inches) with a 240 mm (9.45 inch) going. ## The flight-length difference This is where they diverge most. The US codes limit a flight by maximum vertical rise between landings (147.0 inches under the IRC). The UK and Australia instead limit by the number of risers in a flight — 36 for the UK, 18 for Australia — regardless of the rise height. A calculator built only for one model will mislead users in the other jurisdictions. ## Headroom and width Headroom clusters around 2 metres (78.7 inches) internationally, with the IRC slightly higher at 80.0 inches. Minimum width varies: 36 inches (IRC), 44 inches (IBC), 900 mm in Australia, and no fixed minimum in UK Part K. ## Eurocode is not one code There is no single European stair-dimension table. Eurocode covers structural loading; the geometry rules live in each member state's national regulations. Treat any single "Eurocode stair limit" with caution. Compare the full limits on the codes hub , each with clause citations. ## Worked comparison: the same stair, three codes Take a 7.5-inch riser with a 10-inch tread. Under the US IRC it passes (riser under 7.75, tread at the 10-inch minimum). Under the stricter US IBC commercial standard it fails twice — the riser exceeds 7.0 and the tread is below 11.0. Under the UK's Part K it passes for a private stair (riser under 220 mm). The lesson: a stair is never simply "to code" — it is to code for a specific code under a specific occupancy . ## Flight length: rise vs riser count The deepest divergence is how each code breaks up a tall stair. The US measures the vertical rise between landings (147 inches under the IRC). The UK and Australia count risers per flight instead — 36 and 18 respectively. For a tall flight this produces different landing positions: a US designer adds a landing when the rise crosses 147 inches; a UK designer adds one at the 36th riser regardless of how tall those risers are. ## Why editions matter as much as countries Even within one country the edition your local authority enforces decides the numbers. The IRC's stair geometry has held steady across the 2018, 2021, and 2024 editions, but the 2024 edition renumbered the stairway section (from R311.7 to R318.7), so a clause citation that was correct last year may point to the wrong number now. Always confirm both the code and the edition adopted in your jurisdiction before relying on a figure. ## Eurocode is not a single table Unlike the IRC or Part K, the Eurocode framework sets no single prescriptive stair-dimension table. Individual member states define their own stair geometry through national rules, so "Eurocode" figures vary country to country. Treat any single Eurocode number as an estimate and verify against the relevant national annex. ## Related guides Stair Headroom Rules and How to Measure · Stair Landing Requirements · The Blondel Comfort Rule for Stairs URL: https://staircalculators.net/guides/stair-stringer-layout/ Home / Guides / Laying Out a Stair Stringer Guide # Laying Out a Stair Stringer ## The framing square method A stringer is marked with a framing square set to the riser on one leg and the tread on the other. Stair gauges (small clamps) lock those two numbers so every step is identical as you step the square down the board. Uniformity matters: the IRC allows no more than 3/8 inch variation between the tallest and shortest riser in a flight. ## Riser and tread marks Mark each step by sliding the square along the board edge, aligning the locked riser and tread points, and tracing the corner. Repeat for every step. The number of full notches equals the number of treads, which is one fewer than the riser count. ## How long does the stringer board need to be? Before you mark anything, you need a board long enough to hold the whole diagonal. The structural stringer length is the hypotenuse of the rise-run triangle — the straight-line distance from the top of the flight to the bottom. stringer length = √(total rise² + total run²) For a 108-inch total rise over a 130-inch run, that is √(108² + 130²) = about 169 inches, or roughly 14 feet. Always buy longer than the bare diagonal: add 12 to 16 inches of extra length to cover the triangular offcuts lost at the top plumb cut (where the stringer meets the header or ledger) and the bottom level cut (where it lands on the pad). Running short on a stringer board is a common and avoidable waste of an expensive 2x12. ## The two cut angles Every stringer has two repeating cut angles. The plumb cut (vertical, where the stringer seats against the header and where each riser face sits) matches the stair pitch. The level cut (horizontal, where each tread sits and where the bottom foot lands) is the complement. plumb angle = atan(unit rise / unit tread) level angle = 90° − plumb angle These are the angles your framing square reproduces automatically when you set it to the riser and tread — you rarely cut to a protractor reading, but knowing the pitch helps when you set a saw bevel for the top and bottom cuts. ## The bottom-riser deduction The first riser must be shortened by the thickness of one tread, otherwise the bottom step ends up taller than the rest once treads are installed. This "dropping the stringer" step is a classic first-timer mistake that produces an uneven bottom step. ## Watch the throat After notching, at least 3.5 inches of sound wood must remain behind each notch on a cut stringer. If the layout leaves less, the board is too small for the step geometry — move up from a 2x10 to a 2x12. A 1:1 printable template removes most of this marking risk by letting you trace the actual notch layout directly onto the board. Size the stringer first in the straight stair calculator . throat depth = board depth − notch height (≥ 3.5 in for a cut stringer) bottom riser cut = layout riser − tread thickness ## Why the throat matters The throat is the band of solid wood left behind each notch, measured perpendicular to the board's back edge. Cut too deep and the stringer becomes a row of weak triangles that can split under load. The IRC-backed rule of thumb is at least 3.5 inches of throat, which for normal step geometry rules out a 2x10 and pushes you to a 2x12. Always check the throat your geometry leaves before buying lumber — it's the difference between a stiff stair and a springy, unsafe one. ## Cut vs housed stringers A cut (open) stringer has the steps notched out of the top edge, with treads sitting on the cut. A housed (closed) stringer keeps the board solid and routs shallow tapered pockets into its inside face, into which the treads and risers are wedged and glued. Housed stringers are stronger and quieter (no throat to weaken them) but require a router and template; cut stringers are faster and the standard for deck and basement stairs. ## Marking accurately Small errors compound across a flight. Trace each notch with a sharp pencil against the square, not a thick carpenter's marker, and check your locked riser/tread against a tape every few steps in case a gauge slipped. Cut just inside the line and finish the corners by hand. A test fit of the first stringer against the actual rise before cutting the rest saves a wasted board. Get the exact riser, tread, throat, and board recommendation from the stringer calculator . ## Preventing a cracked or split stringer A cut stringer fails at the inside corners of the notches, where the grain is weakest. Two habits prevent it. First, never overcut: stopping the circular saw at the layout lines and finishing the corner with a handsaw keeps the throat intact — an overcut kerf that runs past the corner is a built-in crack waiting to open under load. Second, keep enough throat (at least 3.5 inches of solid wood behind the deepest notch), which a 2x12 provides for normal step geometry but a 2x10 often does not. If a stringer does split, the safe fix is to replace it rather than glue or screw it back — a repaired stringer can't be trusted with live load. For wide stairs, adding an extra mid-span stringer reduces the load each one carries and the chance of a future split. ## Related guides Dropping the Stringer: Why the Bottom Step Is Shorter · How to Build Deck Stairs (Step by Step) · Rise and Run Explained · How Many Steps for a Given Ceiling Height? URL: https://staircalculators.net/guides/winder-geometry-explained/ Home / Guides / Winder Stair Geometry Explained Guide # Winder Stair Geometry Explained ## What makes a winder different A winder stair turns without a flat landing by using pie-shaped treads — narrow at the inside of the turn, wide at the outside. They save floor area, which is why they are common in loft conversions and tight stairwells, but their geometry is where inexperienced builders get caught. ## The walking line Because each winder tread is a wedge, its depth changes with how far out you measure. Codes define a walking line at a fixed offset from the narrow side — 12.0 inches under the IRC — and require the tread depth along that line to be at least 10.0 inches. The depth at any radius equals that radius times the angle the tread sweeps, in radians. tread depth = radius × (turn angle / number of treads) in radians ## The narrow-end trap The most common winder failure is a narrow end that pinches below the minimum — 6.0 inches under the IRC. A tight inner newel radius or too many treads crammed into the turn shrinks that narrow point. The fixes are to widen the inner radius, reduce the turn angle, or use fewer winder treads. ## Designing one that passes Start from the turn angle (often 90 degrees) and a tread count, then check both the narrow end and the walking line. If either falls short, adjust one variable at a time. The winder calculator shows all three depths live and flags each against your selected code. walking-line depth = radius × (sweep angle in radians) ≥ 10 in narrow-end depth ≥ 6 in (IRC) ## How to fix a pinched narrow end When the narrow end of a pie tread falls below the 6-inch minimum, you have three levers. Increase the inner newel radius so the narrow edge starts further from the center. Reduce the turn angle each tread sweeps by using more winder treads across the turn (three 30-degree treads instead of two 45-degree ones). Or widen the stair so the whole wedge grows. Usually a combination of a fatter newel and more treads solves it. ## Winders vs a landing A winder turns within the run, saving the floor area a landing would consume — the reason they appear in lofts and tight stairwells. The cost is geometry: pie treads are harder to climb safely (your foot meets a different depth depending on where you step) and harder to build and inspect than a simple landing. If you have the floor space, a landing-based quarter- or half-turn is the more forgiving choice; if you don't, winders are how you make the turn fit. ## Three-tread vs two-tread turns A 90-degree turn is most often made with three winder treads sweeping 30 degrees each, which keeps the walking-line depth reasonable. Two 45-degree treads save a step but sweep so much angle that the walking-line depth gets shallow and the narrow end pinches. More treads across the turn almost always gives a safer, more code-compliant winder. Check narrow-end and walking-line depth automatically in the winder calculator . ## Related guides How to Size a Spiral Staircase · Stair Codes by Country: A Comparison · Stair Landing Requirements ============================================================ BUILDING CODES ============================================================ URL: https://staircalculators.net/codes/australia-ncc/ Home / Codes / Australia NCC / BCA Code reference # Australian Staircase Calculator (NCC) Stair geometry limits under Australia NCC / BCA, with the governing clause for each and a worked 9-foot example. Then run your own numbers in the calculator. Australian stairs are governed by the National Construction Code (NCC), which incorporates the Building Code of Australia (BCA). The NCC uses metric limits and, like the UK, restricts a flight by riser count rather than by total rise. ## Australia NCC / BCA stair limits Requirement Limit Clause Max riser height 7.48″ NCC D3D14 Min tread depth 9.45″ NCC D3D14 Min stair width 35.4″ NCC D3D14 Min headroom 78.7″ NCC D3D14 Max risers per flight 18 NCC D3D14 ## Worked example — 9-foot floor-to-floor For a 108-inch total rise under Australia NCC / BCA: dividing by the 7.48-inch maximum riser gives a minimum of 15 risers . Spreading 108 inches evenly across 15 risers yields 7.2 inches per riser — within the limit and uniform, as the code requires. risers = ceil(108 / 7.48) = 15 riser height = 108 / 15 = 7.2″ Run your stair against Australia NCC / BCA ## What's distinctive about the NCC The NCC caps the riser at 190 mm (about 7.48 in) and requires a going of at least 240 mm (about 9.45 in) for typical stairs — slightly gentler risers and deeper treads than the US IRC. Two features stand out compared with US codes: - Flight limited by riser count: a flight is limited to 18 risers before a landing is required, rather than the US approach of capping vertical rise (147 in). - The 2R + G rule: the NCC applies a going/riser relationship to keep stairs comfortable, similar in spirit to the Blondel rule. The NCC also sets a tolerance on riser and going uniformity within a flight, and specifies slip-resistance and the familiar opening rule that restricts gaps in open-riser stairs. A stair designed to US residential numbers (7.75 in riser) will exceed the NCC's 190 mm riser limit and need redesign. ## Other codes Compare with IRC 2018 , IRC 2021 , IRC 2024 , IBC , UK Approved Document K , Eurocode / EN . URL: https://staircalculators.net/codes/eurocode/ Home / Codes / Eurocode / EN (estimate — national annexes govern) Code reference # European Stair Calculator (Eurocode / EN) Stair geometry limits under Eurocode / EN (estimate — national annexes govern), with the governing clause for each and a worked 9-foot example. Then run your own numbers in the calculator. These values are representative estimates, not verified code. Eurocode has no single prescriptive stair table — member-state national rules govern. Confirm locally. ## Eurocode / EN (estimate — national annexes govern) stair limits Requirement Limit Clause Max riser height 7.48″ national annex Min tread depth 9.84″ national annex Min stair width 31.5″ national annex Min headroom 78.7″ national annex Max rise between landings 142.0″ national annex ## Worked example — 9-foot floor-to-floor For a 108-inch total rise under Eurocode / EN (estimate — national annexes govern): dividing by the 7.48-inch maximum riser gives a minimum of 15 risers . Spreading 108 inches evenly across 15 risers yields 7.2 inches per riser — within the limit and uniform, as the code requires. risers = ceil(108 / 7.48) = 15 riser height = 108 / 15 = 7.2″ Run your stair against Eurocode / EN (estimate — national annexes govern) ## Why there is no single "Eurocode stair size" Across the EU, the dimensional geometry of stairs — maximum riser, minimum going, pitch, width — is set by each member state's national building rules and national annexes, not by a pan-European table. Germany's DIN 18065, France's national rules, and others each specify their own figures, and they differ. The figures shown on this page are an estimate of a typical Continental range and must not be relied on for a specific country. ## What Eurocode does govern What the Eurocodes do standardise is structural: EN 1991 (Eurocode 1) sets the imposed loads a stair and its landings must carry — for example characteristic loads for residential and assembly floors and their stairs — and EN 1995 and related parts cover designing the stair structure in timber, steel, or concrete to carry them. So a stair in the EU is typically sized geometrically to the national rule and checked structurally against the relevant Eurocode load case. Practical takeaway: if you need a compliant stair in a specific European country, find that country's national annex or building regulation for the geometry, and use the Eurocode series for the structural loading. Treat any single "Eurocode" dimension as indicative only. ## Other codes Compare with IRC 2018 , IRC 2021 , IRC 2024 , IBC , UK Approved Document K , Australia NCC / BCA . URL: https://staircalculators.net/codes/ibc/ Home / Codes / IBC (US Commercial) Code reference # IBC Commercial Stair Code Calculator Stair geometry limits under IBC (US Commercial), with the governing clause for each and a worked 9-foot example. Then run your own numbers in the calculator. The IBC governs commercial and multi-family stairs in the US — means-of-egress stairways in buildings other than one- and two-family dwellings. Its limits are tighter than the residential IRC because the stairs must safely move larger numbers of people, including under emergency egress. ## IBC (US Commercial) stair limits Requirement Limit Clause Max riser height 7.0″ 1011.5.2 Min tread depth 11.0″ 1011.5.2 Min stair width 44.0″ 1011.2 Min headroom 80.0″ 1011.3 Max rise between landings 144.0″ 1011.6 ## Worked example — 9-foot floor-to-floor For a 108-inch total rise under IBC (US Commercial): dividing by the 7.0-inch maximum riser gives a minimum of 16 risers . Spreading 108 inches evenly across 16 risers yields 6.75 inches per riser — within the limit and uniform, as the code requires. risers = ceil(108 / 7.0) = 16 riser height = 108 / 16 = 6.75″ Run your stair against IBC (US Commercial) ## How the IBC differs from the residential IRC The IBC tightens the two dimensions that matter most for crowd movement: the maximum riser drops to 7.0 inches (from the IRC's 7.75) and the minimum tread rises to 11.0 inches (from 10.0). A stair sized to the residential limit will therefore fail an IBC plan review on both counts — the riser is too tall and the tread too shallow. - Riser: 7.0 in max (IBC) vs 7.75 in (IRC) - Tread: 11.0 in min (IBC) vs 10.0 in (IRC) - Width: typically 44 in min (or 36 in where the occupant load is under 50), vs 36 in residential - Handrails: required on both sides, with extensions at top and bottom Because the envelope is narrower, the comfortable 7×11 pairing that just meets the IRC is the natural target under the IBC. If you are converting a residential design for commercial use, expect to add risers (reducing each riser's height) and deepen treads, which lengthens the total run and changes the footprint. ## Other codes Compare with IRC 2018 , IRC 2021 , IRC 2024 , UK Approved Document K , Australia NCC / BCA , Eurocode / EN . URL: https://staircalculators.net/codes/irc-2018/ Home / Codes / IRC 2018 (US Residential) Code reference # IRC 2018 Stair Code Calculator Stair geometry limits under IRC 2018 (US Residential), with the governing clause for each and a worked 9-foot example. Then run your own numbers in the calculator. IRC 2018 is the residential stair baseline still enforced in many US jurisdictions that have not yet adopted a newer cycle. Its stair geometry sits in Section R311.7, and the dimensional limits below are identical to the 2021 edition — the practical reason to care which edition applies is the clause numbering your inspector will cite, not the numbers themselves. ## IRC 2018 (US Residential) stair limits Requirement Limit Clause Max riser height 7.75″ R311.7.5.1 Min tread depth 10.0″ R311.7.5.2 Min stair width 36.0″ R311.7.1 Min headroom 80.0″ R311.7.2 Max rise between landings 147.0″ R311.7.6 ## Worked example — 9-foot floor-to-floor For a 108-inch total rise under IRC 2018 (US Residential): dividing by the 7.75-inch maximum riser gives a minimum of 14 risers . Spreading 108 inches evenly across 14 risers yields 7.71 inches per riser — within the limit and uniform, as the code requires. risers = ceil(108 / 7.75) = 14 riser height = 108 / 14 = 7.71″ Run your stair against IRC 2018 (US Residential) ## What's specific to the 2018 edition In the 2018 IRC the maximum vertical rise between landings appears at clause R311.7.6. (The 2021 edition kept the same 147-inch limit but renumbered this clause to R311.7.3 as part of a section cleanup.) If your local building department is on the 2018 cycle, cite R311.7.x for stairways — the wholesale move to R318.7 did not happen until the 2024 edition. Because the dimensional envelope is unchanged from 2018 through 2024, a stair that passes here passes the geometry checks in all three editions. What varies between editions is clause numbering and a handful of landing and nosing refinements introduced in 2024, covered on the IRC 2024 page . ## Other codes Compare with IRC 2021 , IRC 2024 , IBC , UK Approved Document K , Australia NCC / BCA , Eurocode / EN . URL: https://staircalculators.net/codes/irc-2021/ Home / Codes / IRC 2021 (US Residential) Code reference # IRC 2021 Stair Code Calculator Stair geometry limits under IRC 2021 (US Residential), with the governing clause for each and a worked 9-foot example. Then run your own numbers in the calculator. IRC 2021 is the most widely adopted residential edition across US jurisdictions as of the mid-2020s. Its stair rules live in Section R311.7. The dimensional limits match both the 2018 and 2024 editions; the 2021 cycle is mainly distinguished by a clause renumber within the stairway section. ## IRC 2021 (US Residential) stair limits Requirement Limit Clause Max riser height 7.75″ R311.7.5.1 Min tread depth 10.0″ R311.7.5.2 Min stair width 36.0″ R311.7.1 Min headroom 80.0″ R311.7.2 Max rise between landings 147.0″ R311.7.3 ## Worked example — 9-foot floor-to-floor For a 108-inch total rise under IRC 2021 (US Residential): dividing by the 7.75-inch maximum riser gives a minimum of 14 risers . Spreading 108 inches evenly across 14 risers yields 7.71 inches per riser — within the limit and uniform, as the code requires. risers = ceil(108 / 7.75) = 14 riser height = 108 / 14 = 7.71″ Run your stair against IRC 2021 (US Residential) ## What changed from IRC 2018 The dimensional limits — 7.75-inch maximum riser, 10-inch minimum tread, 36-inch width, 80-inch headroom, 147-inch maximum rise between landings — are unchanged from the 2018 edition. The notable housekeeping change is that the vertical-rise-between-landings provision was renumbered from R311.7.6 (2018) to R311.7.3 (2021). The walkline definition for winder treads at R311.7.4 was also clarified. If you are moving from a 2018-based plan set, no stair dimension needs to change for the 2021 code — only the clause references on your drawings. The larger renumber to R318.7 comes in the 2024 edition . ## Other codes Compare with IRC 2018 , IRC 2024 , IBC , UK Approved Document K , Australia NCC / BCA , Eurocode / EN . URL: https://staircalculators.net/codes/irc-2024/ Home / Codes / IRC 2024 (US Residential) Code reference # IRC 2024 Stair Code Calculator Stair geometry limits under IRC 2024 (US Residential), with the governing clause for each and a worked 9-foot example. Then run your own numbers in the calculator. IRC 2024 reorganized Chapter 3, moving the entire stairway section from R311.7 to R318.7 . The dimensional limits stayed the same, but the 2024 edition introduced a few substantive refinements to nosing tolerance and landing exceptions that are worth knowing if your jurisdiction has adopted this cycle. ## IRC 2024 (US Residential) stair limits Requirement Limit Clause Max riser height 7.75″ R318.7.5.1 Min tread depth 10.0″ R318.7.5.2 Min stair width 36.0″ R318.7.1 Min headroom 80.0″ R318.7.2 Max rise between landings 147.0″ R318.7.3 ## Worked example — 9-foot floor-to-floor For a 108-inch total rise under IRC 2024 (US Residential): dividing by the 7.75-inch maximum riser gives a minimum of 14 risers . Spreading 108 inches evenly across 14 risers yields 7.71 inches per riser — within the limit and uniform, as the code requires. risers = ceil(108 / 7.75) = 14 riser height = 108 / 14 = 7.71″ Run your stair against IRC 2024 (US Residential) ## What changed from IRC 2021 The headline change is structural: stairways were renumbered from R311.7 to R318.7 when Chapter 3 was reorganized. A clause that read R311.7.5.1 in 2021 is R318.7.5.1 in 2024. The core dimensional limits did not change. Two substantive refinements are worth noting: - Nosing uniformity (R318.7.5.3): the 3/8-inch minimum/maximum tolerance for nosing projections now applies to each individual flight and its upper landing, rather than across the entire stairway. This is more forgiving for stairs split by landings. - Landing exceptions (R318.7.6): new exceptions allow the top landing of an interior stairway to be on the other side of a door at the top of the stairs; permit a garage top-landing up to 7¾ inches below the door threshold; and waive the top landing for an exterior stairway of not more than two risers. For everyday stair sizing the numbers are identical to IRC 2021 — if your stair passes there, it passes here. Update clause citations to the R318.7 series and check the new nosing and landing allowances if they affect your layout. ## Other codes Compare with IRC 2018 , IRC 2021 , IBC , UK Approved Document K , Australia NCC / BCA , Eurocode / EN . URL: https://staircalculators.net/codes/uk-part-k/ Home / Codes / UK Approved Document K (Private) Code reference # UK Stair Regulations Calculator (Part K) Stair geometry limits under UK Approved Document K (Private), with the governing clause for each and a worked 9-foot example. Then run your own numbers in the calculator. In England and Wales, stairs are governed by Approved Document K of the Building Regulations (Scotland uses Section 4 of the Technical Handbooks with similar figures). Part K is structured differently from US codes: instead of one residential limit, it defines three stair categories, each with its own rise and going limits. ## UK Approved Document K (Private) stair limits Requirement Limit Clause Max riser height 8.66″ ADK 1.2 Min tread depth 8.66″ ADK 1.2 Min headroom 78.7″ ADK 1.10 Max risers per flight 36 ADK 1.16 Max pitch 42° ADK 1.2 ## Worked example — 9-foot floor-to-floor For a 108-inch total rise under UK Approved Document K (Private): dividing by the 8.66-inch maximum riser gives a minimum of 13 risers . Spreading 108 inches evenly across 13 risers yields 8.31 inches per riser — within the limit and uniform, as the code requires. risers = ceil(108 / 8.66) = 13 riser height = 108 / 13 = 8.31″ Run your stair against UK Approved Document K (Private) ## The three Part K stair categories Part K sets dimensional limits by stair type rather than a single residential figure. Getting the category right is the most common compliance question on UK projects: - Private (one dwelling): max rise 220 mm, min going 220 mm, max pitch 42°. - Utility (escape, access for maintenance): max rise 190 mm, min going 250 mm. - General access (public / common stairs in flats and non-dwellings): max rise 170 mm, min going 250 mm. A stair serving more than one dwelling is a common stair and must meet the general-access limits (170 mm rise, 250 mm going) — not the more generous private limits. Using a 220 mm rise on a shared stair is among the most frequent failures on HMO and flat-conversion projects. ## Other Part K rules to know Part K also applies the "2R + G" comfort rule, expecting twice the rise plus the going to fall between 550 and 700 mm. Open risers must not allow a 100 mm sphere to pass, with treads overlapping at least 16 mm. A private flight is generally limited to 16 risers before a landing is required, and minimum headroom is 2.0 m (relaxed to 1.8 m at the centre for constrained loft conversions). ## Other codes Compare with IRC 2018 , IRC 2021 , IRC 2024 , IBC , Australia NCC / BCA , Eurocode / EN . ============================================================ CALCULATORS ============================================================ URL: https://staircalculators.net/calculators/ada-ramp/ Home / Calculators / ADA ramp calculator Calculator # ADA ramp calculator Ramp run length, slope, and required landings for a given rise, using the 1:12 maximum slope. ADA values are based on the 2010 ADA Standards and provided as estimates. Verify against the current governing standard before relying on these for compliance. ADA ramp calculator Vertical rise in Slope 1:N Project name (for PDF) ✎ Ramp slope Results ↓ Download full PDF Run — Slope — Segments — Landings — ## ADA ramp slope The 2010 ADA Standards cap ramp slope at 1:12 (about 8.33%). A single ramp run may rise no more than 30 inches before a level landing is required. This calculator gives the run length, segment count, and landings. run = rise × N (slope 1:N) max slope 1:12 ; max 30" rise per run ## Frequently asked questions ### What is the maximum ADA ramp slope? 1:12, or about 8.33 percent, under the 2010 ADA Standards. Steeper ramps are not compliant for new construction. ### How long can an ADA ramp run be? A single run may rise no more than 30 inches before a level landing is required. ### How wide must an ADA ramp be? At least 36 inches of clear width between handrails under the 2010 ADA Standards. URL: https://staircalculators.net/calculators/ada-stair/ Home / Calculators / ADA stair calculator Calculator # ADA stair calculator Check riser and tread against ADA 504 requirements (riser 4-7 inches, tread minimum 11 inches). ADA values are based on the 2010 ADA Standards and provided as estimates. Verify against the current governing standard before relying on these for compliance. ADA stair calculator Total rise in Target riser in Tread depth in Project name (for PDF) ✎ ADA stair elevation Results ↓ Download full PDF Steps — Riser — Tread — ## ADA stair geometry ADA 504 requires uniform risers between 4 and 7 inches and treads of at least 11 inches, with specific nosing and handrail provisions. This checks the core riser and tread numbers. ## Frequently asked questions ### What are ADA stair requirements? ADA 504 requires uniform riser heights of 4 to 7 inches, tread depths of at least 11 inches, specific nosing profiles, and handrails on both sides. ### Is a 7-inch riser ADA compliant? Yes, 7 inches is the maximum allowed riser under ADA 504. Risers must be uniform within the flight. ### Do ADA stairs need handrails on both sides? Yes, ADA 505 requires handrails on both sides of stairs, with extensions at the top and bottom. ## How ADA stairs differ from ordinary stairs Stairs on an accessible route in covered facilities follow tighter rules than a typical residential stair. Risers and treads must be uniform, open risers are not permitted, and the tread surface must be slip-resistant. Handrails are required on both sides, mounted at a consistent height, and must extend horizontally beyond the top and bottom risers so a user has something to hold before and after the steps. This calculator sizes the flight to those expectations — uniform risers across the total rise, a compliant tread depth, and the handrail extensions — so the result reflects accessible-egress practice rather than the looser residential minimums. Always confirm the specific figures against the ADA Standards and the building code edition your jurisdiction enforces, since accessible-route requirements carry legal weight. URL: https://staircalculators.net/calculators/baluster-spacing/ Home / Calculators / Baluster spacing calculator Calculator # Baluster spacing calculator Space balusters so a 4-inch sphere cannot pass. Enter your rail length and baluster width to get the count and exact gap. Baluster spacing calculator Building code IRC 2021 (US Residential) IRC 2018 IRC 2024 IBC (US Commercial) UK Part K Australia NCC Eurocode (estimate) Rail run length in Baluster width in Project name (for PDF) ✎ Baluster layout Results ↓ Download full PDF Balusters — Clear gap — Spacing o.c. — Gaps — ## The 4-inch sphere rule Building codes require that a 4-inch sphere cannot pass between balusters, to protect small children. This calculator finds the smallest number of evenly spaced balusters that keeps every clear gap under 4 inches for your rail length and baluster width. clear gap = (rail length − n × baluster width) / (n + 1) increase n until clear gap < 4" ## Frequently asked questions ### What is the 4-inch sphere rule? Codes require that a 4-inch sphere cannot pass through the gap between balusters, anywhere on a guard or stair rail, to prevent a child from slipping through. ### How do I calculate baluster spacing? Divide the rail into equal gaps so each clear opening is under 4 inches. For n balusters there are n+1 gaps; the clear gap is the rail length minus the total baluster width, divided by the number of gaps. ### What is the standard baluster width? Metal balusters are commonly 0.5 to 0.75 inches; wood balusters are often 1.25 inches. Wider balusters need slightly fewer pieces for the same rail. URL: https://staircalculators.net/calculators/concrete/ Home / Calculators / Concrete stair calculator Calculator 07 # Concrete stair calculator Poured concrete stairs: volume in cubic yards and metres, formwork area, and a rebar length estimate. Concrete stair calculator Code IRC 2018 (US) IRC 2021 (US) IRC 2024 (US) IBC (US Commercial) UK Part K Eurocode (est.) AU NCC Total rise in Target riser in Tread depth in Stair width in Waist (slab) thickness in Project name (for PDF) ✎ Elevation — side view Results ↓ Download full PDF Steps — Riser — Volume yd³ — Volume m³ — Formwork ft² — Rebar ft — ## Estimating a concrete pour Poured-concrete stair volume is the sum of the step triangles plus the structural waist slab running up the incline. The calculator returns volume in both cubic yards (US ready-mix ordering) and cubic metres, plus a formwork area estimate and a rough rebar length. Always order a little extra concrete to allow for spillage and uneven subgrade. step volume = ½ × riser × tread × width × steps waist volume = thickness × incline length × width 1 yd³ = 27 ft³ = 46,656 in³ Rebar is a rough estimate, not a structural design. Have poured stairs engineered where required. URL: https://staircalculators.net/calculators/curved/ Home / Calculators / Curved stair calculator Calculator # Curved stair calculator Arc-tread geometry for a curved stair: centerline radius, walkline tread depth, and step angle. This is a planning estimate only. Cantilever and curved stairs require engineered support; loads must be verified by a qualified engineer. Curved stair calculator Building code IRC 2021 (US Residential) IRC 2018 IRC 2024 IBC (US Commercial) UK Part K Australia NCC Eurocode (estimate) Total rise in Target riser in Inner radius in Stair width in Arc swept ° Project name (for PDF) ✎ Curved plan Results ↓ Download full PDF Steps — Riser — Walkline tread — Step angle — C/L radius — ## Curved stair geometry A curved stair sweeps treads along an arc of constant radius (unlike a spiral, which wraps a tight column). Tread depth is measured along the walking line near the centerline of the stair. The step angle is the arc each tread sweeps. centerline radius = inner radius + width/2 walkline tread = (centerline radius × arc) / treads ## Frequently asked questions ### What is the difference between a curved and a spiral stair? A curved stair follows a large, gentle arc with two open sides and no central column; a spiral wraps tightly around a center column. Curved stairs are easier to walk but need much more space. ### How is curved stair tread depth measured? Along the walking line, typically near the centerline of the stair width, since the tread is wider at the outer edge and narrower at the inner edge. ### Do curved stairs need engineering? Yes. The curved stringers are complex structural and joinery elements and should be engineered and shop-fabricated. URL: https://staircalculators.net/calculators/deck-stair/ Home / Calculators / Deck stair calculator Calculator 02 # Deck stair calculator Size deck stair stringers from grade to deck: riser, tread, board recommendation, stringer count and landing triggers. Deck stair calculator Code IRC 2018 (US) IRC 2021 (US) IRC 2024 (US) IBC (US Commercial) UK Part K Eurocode (est.) AU NCC Total rise (grade to deck) in Total run available in Target riser in Stair width in Stringer spacing (OC) in Project name (for PDF) ✎ Elevation — side view Results ↓ Download full PDF Steps — Riser — Tread — Board — Stringers — Throat 2x12 — ## Deck stair specifics Deck stairs add three concerns to the basic geometry. First, the stringer board must keep at least 3.5 inches of sound wood behind each notch — the throat. If a 2x10 can't hold that, the calculator calls for a 2x12. Second, stringer spacing of 16 or 24 inches on-center determines how many stringers the width needs. Third, a single flight may not exceed the code's maximum rise between landings; cross that and the tool flags that a landing is required. throat = board depth − (riser × tread) / √(riser² + tread²) stringers = ceil(width / spacing) + 1 Compliance thresholds are pending primary-source verification. Confirm against your enforced code edition before cutting. URL: https://staircalculators.net/calculators/deck-stringer/ Home / Calculators / Deck stringer calculator Calculator 02 # Deck stringer calculator Lay out deck stair stringers: board size (2x10 vs 2x12), throat depth, stringer count and spacing, with the cut geometry for an outdoor flight. Deck stair calculator Code IRC 2018 (US) IRC 2021 (US) IRC 2024 (US) IBC (US Commercial) UK Part K Eurocode (est.) AU NCC Total rise (grade to deck) in Total run available in Target riser in Stair width in Stringer spacing (OC) in Project name (for PDF) ✎ Elevation — side view Results ↓ Download full PDF Steps — Riser — Tread — Board — Stringers — Throat 2x12 — ## Laying out deck stringers The stringer is the notched board that carries the treads. This calculator focuses on the stringer side of a deck stair : board recommendation, throat depth, stringer count, and cut length. ## Frequently asked questions ### What size board do I need for deck stair stringers? A cut stringer must keep at least 3.5 inches of sound wood behind each notch; most need a 2x12. ### How many stringers does a deck stair need? At 16-inch spacing, divide width by 16 and add one. ### How far apart should deck stringers be? Commonly 16 inches on-center for standard decking. URL: https://staircalculators.net/calculators/double-winder/ Home / Calculators / Double-winder stair calculator Calculator 05 # Double-winder stair calculator A double-winder turns 180° using two sets of pie-shaped winder treads instead of a landing. Check narrow-end and walking-line depths to code. Winder stair calculator Code IRC 2018 (US) IRC 2021 (US) IRC 2024 (US) IBC (US Commercial) UK Part K Eurocode (est.) AU NCC Total rise in Target riser in Inner radius (newel) in Stair width in Turn angle ° Winder treads # Project name (for PDF) ✎ Plan — winder treads Results ↓ Download full PDF Steps — Riser — Step angle — Narrow depth — Walk-line depth — Wide depth — ## What is a double-winder stair? A double-winder reverses direction through 180 degrees entirely on winder treads — two winder sets rather than the single 90° turn of a standard winder stair . ## Frequently asked questions ### What is a double-winder stair? A staircase that turns 180 degrees using two sets of pie-shaped winder treads instead of landings. ### Are double-winder stairs harder to make code-compliant? Yes. With more pie treads across a tighter turn, the narrow ends are more likely to fall below minimum depth. ### How many treads does a double-winder use? Commonly five to seven across a 180° turn, depending on inner radius and code. URL: https://staircalculators.net/calculators/floating/ Home / Calculators / Floating stair calculator Calculator # Floating stair calculator Plan tread count, riser, and cantilever reach for a floating stair. Structural support must be engineered. This is a planning estimate only. Cantilever and curved stairs require engineered support; loads must be verified by a qualified engineer. Floating stair calculator Building code IRC 2021 (US Residential) IRC 2018 IRC 2024 IBC (US Commercial) UK Part K Australia NCC Eurocode (estimate) Total rise in Target riser in Tread depth in Tread width in Project name (for PDF) ✎ Floating stair Results ↓ Download full PDF Steps — Riser — Tread — Cantilever — ## Floating stair planning Floating (cantilever) stairs appear to project from a wall or a central spine with no visible support. The geometry is the same as a straight stair; the difference is structural. Each tread cantilevers and must be engineered for load. ## Frequently asked questions ### How do floating stairs support weight? Through an engineered system, commonly a hidden steel spine, wall-embedded steel, or a mono-stringer. Each tread cantilevers and must be sized for load by an engineer. ### Are floating stairs code compliant? The geometry (riser, tread, headroom) follows the same code as any stair; the open risers must still reject a 4-inch sphere, and a guard or rail is required. The structure needs engineering. ### How thick are floating treads? Thick enough to carry the cantilever load, often 2 to 3 inches for hardwood over a steel core. An engineer sizes them. URL: https://staircalculators.net/calculators/half-turn/ Home / Calculators / Half-turn stair calculator Calculator 04 # Half-turn stair calculator A half-turn stair reverses direction through 180° around a half-landing. Solve the two parallel flights, the landing, and the stairwell footprint. U-shape stair calculator Code IRC 2018 (US) IRC 2021 (US) IRC 2024 (US) IBC (US Commercial) UK Part K Eurocode (est.) AU NCC Total rise in Target riser in Tread depth in Stair width in Well gap in Project name (for PDF) ✎ Plan — half turn Results ↓ Download full PDF Steps — Riser — Lower flight — Upper flight — Footprint X — Footprint Y — ## What is a half-turn stair? A half-turn staircase doubles back on itself through 180 degrees, with the two flights running parallel and a half-landing connecting them. It is the same configuration commonly called a U-shaped stair . ## Frequently asked questions ### Is a half-turn stair the same as a U-shaped stair? Yes. Both describe a staircase that reverses 180 degrees around a landing, with parallel flights. ### Why choose a half-turn stair? It gives the most compact floor footprint for a given rise. ### What is the difference between a half-turn and a switchback? They are essentially the same 180° reversal; the terms differ by context. URL: https://staircalculators.net/calculators/handrail/ Home / Calculators / Handrail calculator Calculator # Handrail calculator Rail length along the rake, end returns, and a height check against your code. Handrail calculator Building code IRC 2021 (US Residential) IRC 2018 IRC 2024 IBC (US Commercial) UK Part K Australia NCC Eurocode (estimate) Total rise in Total run in Handrail height in Project name (for PDF) ✎ Handrail elevation Results ↓ Download full PDF Rake length — Total w/ returns — Height — Min — Max — ## Handrail length and height The graspable rail runs the diagonal length of the flight (the rake), plus end extensions or returns required for safety. Height is measured vertically from the tread nosing line and must sit within the code band. rake = √(rise² + run²) handrail height: 34–38" above nosing (IRC) ## Frequently asked questions ### How long should a handrail be? At least the diagonal length of the flight, plus any required top and bottom extensions or returns. Commercial codes often require a 12-inch extension at the top and one tread-depth plus 12 inches at the bottom. ### What height should a stair handrail be? Between 34 and 38 inches above the tread nosing line under the IRC and IBC. ### Do handrails need returns? Many codes require the rail to return to the wall or post at each end so clothing or bags cannot catch on an open end. URL: https://staircalculators.net/calculators/headroom/ Home / Calculators / Stair headroom calculator Calculator # Stair headroom calculator Check headroom clearance and the floor-opening length you need so the stair maintains the code minimum all the way up. Stair headroom calculator Building code IRC 2021 (US Residential) IRC 2018 IRC 2024 IBC (US Commercial) UK Part K Australia NCC Eurocode (estimate) Total rise in Total run in Target riser in Floor assembly above in Project name (for PDF) ✎ Headroom section Results ↓ Download full PDF Min headroom — Required opening — Angle — Steps — ## Headroom and the floor opening Headroom is the vertical clearance measured from the tread nosing line. It is most often pinched at the floor opening at the top of the stair. This calculator gives the code minimum and the opening length needed so a climber clears the floor edge above all the way up. required opening = (floor assembly + min headroom) / tan(angle) ## Frequently asked questions ### What is the minimum stair headroom? The IRC requires at least 80 inches (6 feet 8 inches) measured vertically from the tread nosing line, at every point along the stair. ### How is stair headroom measured? Vertically, from a line connecting the tread nosings up to the ceiling or floor structure above. Inspectors check it along the whole flight, not just the ends. ### How do I fix insufficient headroom? Lengthen the floor opening, move the stair start point, or reduce the pitch so it reaches the opening sooner. Headroom is set by framing, so fix it at design stage. URL: https://staircalculators.net/calculators/l-shape/ Home / Calculators / L-shape stair calculator Calculator 03 # L-shape stair calculator Quarter-turn stairs with a landing: solve the riser split between flights, landing size, and the combined floor footprint. L-shape stair calculator Code IRC 2018 (US) IRC 2021 (US) IRC 2024 (US) IBC (US Commercial) UK Part K Eurocode (est.) AU NCC Total rise in Target riser in Tread depth in Stair width in Landing after step (0=auto) # Project name (for PDF) ✎ Plan — quarter turn Results ↓ Download full PDF Steps — Riser — Lower flight — Upper flight — Footprint X — Footprint Y — ## The quarter-turn landing An L-shape stair turns 90 degrees at a landing. The risers split across two flights; the landing replaces a tread and must be at least as deep as the stair is wide. The combined footprint is the lower flight run plus landing in one direction, and the upper flight run plus stair width in the other. Landing depth must be ≥ stair width. Compliance thresholds pending verification. ## How an L-shaped stair is sized An L-shaped (quarter-turn) stair makes a single 90-degree turn at a landing, typically partway up the flight. It tucks a staircase into a corner, breaks the climb into two shorter runs, and gives a natural place to pause — which is why it is a popular choice for both homes and the landings that long flights require anyway. The calculator divides your total rise into uniform risers across the two flights and sizes the corner landing. Under the IRC that landing must be at least as deep as the stair is wide and no less than 36 inches in the direction of travel. Choosing where the turn falls lets you balance the two flight lengths to fit the room; the landing itself replaces one tread and consumes a square of floor roughly the stair width on each side. URL: https://staircalculators.net/calculators/landing-size/ Home / Calculators / Stair landing size calculator Calculator # Stair landing size calculator Find the minimum landing depth for your stair. Codes require at least the stair width, and never less than 36 inches in the direction of travel. Stair landing size calculator Building code IRC 2021 (US Residential) IRC 2018 IRC 2024 IBC (US Commercial) UK Part K Australia NCC Eurocode (estimate) Stair width in Door swing onto landing in Project name (for PDF) ✎ Landing plan Results ↓ Download full PDF Min depth — With door — Min width — ## Landing size requirements A landing must be at least as deep, in the direction of travel, as the stair is wide, and never less than 36 inches under the IRC. Where a door swings onto the landing, the depth must also clear the swing so no one is pushed toward the steps. min landing depth = max(stair width, 36") ## Frequently asked questions ### How deep must a stair landing be? At least as deep as the stair is wide, and never less than 36 inches in the direction of travel under the IRC. ### Does a door change the landing size? Yes. If a door swings over the landing, the landing must be deep enough that the swing does not push a person toward the stairs. ### Is a landing required for every staircase? Not every one, but a landing is required where a flight exceeds the maximum rise between landings, or to change direction in L- and U-shaped stairs. URL: https://staircalculators.net/calculators/load-capacity/ Home / Calculators / Stair load calculator Calculator # Stair load calculator The design live load your stair must be built to carry under code, and the total that implies for the stair area. This shows the design live load the code requires a stair to carry — not the capacity of a built stair. Actual capacity depends on materials, spans, and connections and must be verified by a qualified engineer. Stair load calculator Stair width in Total run in Project name (for PDF) ✎ Load area Results ↓ Download full PDF Live load — Concentrated — Plan area ft2 — Total uniform — ## Stair design live load Building codes set the minimum live load a stair must be designed to carry. Residential stairs use 40 psf (pounds per square foot) plus a 300 lb concentrated load; commercial and assembly stairs use 100 psf. This calculator gives that design load and the uniform total over the stair plan area. It does not tell you what a built stair will hold — that is capacity, which requires structural engineering. total uniform load = plan area (ft²) × live load (psf) ## Frequently asked questions ### What live load are stairs designed for? Residential stairs are designed for 40 psf plus a 300 lb concentrated load under the IRC; commercial and assembly stairs for 100 psf under the IBC. ### Does this tell me how much weight my stairs can hold? No. This is the design load the code requires, not the capacity of a built stair. Real capacity depends on materials, spans, and connections, and must be checked by an engineer. ### What is a concentrated load on a stair? A single point load (300 lb under the IRC) applied to the worst-case spot, representing a heavy individual or object, checked in addition to the uniform load. URL: https://staircalculators.net/calculators/newel-post/ Home / Calculators / Newel post calculator Calculator # Newel post calculator Find how many newel posts a rail run needs and their spacing, with end posts included. Newel post calculator Building code IRC 2021 (US Residential) IRC 2018 IRC 2024 IBC (US Commercial) UK Part K Australia NCC Eurocode (estimate) Rail run length in Max spacing o.c. in Project name (for PDF) ✎ Newel layout Results ↓ Download full PDF Posts — Intermediate — Spacing — ## Newel post spacing Newel posts anchor the handrail at the ends and at intervals along a long run. Spacing is limited by structural rigidity, commonly around six feet on center, with posts always at both ends. ## Frequently asked questions ### How far apart should newel posts be? Commonly no more than about 6 feet on center for rigidity, with a post at each end of the run and at every change of direction. ### Do I need intermediate newel posts? On long runs, yes, to keep the handrail rigid. Short runs may only need the two end posts. ### Where do newel posts go on stairs? At the bottom and top of each flight, and at landings where the rail changes direction. ## What the newel calculation tells you Newel posts anchor a handrail and resist the sideways load a person puts on it, so they cannot be spaced arbitrarily. This calculator takes your run length and a maximum spacing and returns how many posts you need and how they space out evenly — always including a post at each end, where the rail starts and terminates. As a rule of thumb, a structural newel every 6 feet or so keeps a residential rail from flexing, with posts always landing at the top, the bottom, and at any change of direction such as a landing. Decorative balusters fill the gaps between newels and follow the separate 4-inch sphere spacing rule, which the baluster spacing calculator handles. URL: https://staircalculators.net/calculators/nosing/ Home / Calculators / Stair nosing calculator Calculator # Stair nosing calculator Check nosing overhang and the effective tread depth it adds. Confirm the projection sits within code when the tread board is shallow. Stair nosing calculator Building code IRC 2021 (US Residential) IRC 2018 IRC 2024 IBC (US Commercial) UK Part K Australia NCC Eurocode (estimate) Tread board depth in Nosing projection in Project name (for PDF) ✎ Nosing detail Results ↓ Download full PDF Effective tread — Nosing min — Nosing max — ## Nosing and effective tread The nosing is the part of the tread that projects beyond the riser below. When a tread board is shallower than the code minimum, the nosing makes up the effective walking depth. The projection itself is capped so it is not a trip hazard. effective tread = tread board depth + nosing projection ## Frequently asked questions ### What is stair nosing? The rounded or square front edge of a tread that overhangs the riser below it, adding walking depth and reducing toe-stubbing. ### How much can a stair nosing project? Under the IRC, when nosing is required the projection must be between 0.75 and 1.25 inches. It must also be consistent within a flight. ### When is nosing required? When the tread depth alone is less than the code minimum (10 inches under the IRC), the nosing makes up the effective depth. With deep enough treads, nosing is optional. URL: https://staircalculators.net/calculators/quarter-turn/ Home / Calculators / Quarter-turn stair calculator Calculator 03 # Quarter-turn stair calculator A quarter-turn stair makes a single 90° change of direction at a landing. Size both flights, the landing, and the footprint, with live code checks. L-shape stair calculator Code IRC 2018 (US) IRC 2021 (US) IRC 2024 (US) IBC (US Commercial) UK Part K Eurocode (est.) AU NCC Total rise in Target riser in Tread depth in Stair width in Landing after step (0=auto) # Project name (for PDF) ✎ Plan — quarter turn Results ↓ Download full PDF Steps — Riser — Lower flight — Upper flight — Footprint X — Footprint Y — ## What is a quarter-turn stair? A quarter-turn staircase turns 90 degrees partway up, using a flat landing at the corner rather than angled winder treads. It is the same geometry the building trades also call an L-shaped stair — the two terms are interchangeable. "Quarter-turn" describes the 90° rotation; "L-shaped" describes the plan outline. ## Frequently asked questions ### Is a quarter-turn stair the same as an L-shaped stair? Yes. Both describe a staircase that turns 90 degrees at a landing. The calculation is identical. ### How big must the landing be on a quarter-turn stair? At least as deep as the stair is wide, and never less than 36 inches in the direction of travel under the IRC. ### How is a quarter-turn different from a winder? A quarter-turn uses a flat landing to turn; a winder uses pie-shaped treads. URL: https://staircalculators.net/calculators/rise-over-run/ Home / Calculators / Rise over run calculator Calculator 08 # Rise over run calculator Quick slope utility: enter rise and run to get angle, percent grade, ratio, 1-in-N, and the diagonal length. Rise over run calculator Rise in Run in Project name (for PDF) ✎ Slope triangle Results ↓ Download full PDF Percent — Ratio — 1 in N — Diagonal — Angle — ## Slope every which way The same slope can be written as an angle, a percent grade, a ratio, or as "1 in N". This utility converts between them and gives the diagonal length by the Pythagorean theorem. Useful for stairs, ramps, handrails and grading. angle = atan(rise / run) percent = (rise / run) × 100 1 in N where N = run / rise diagonal = √(rise² + run²) ## Reading the four outputs The four ways of writing a slope each suit a different trade. Angle (degrees from horizontal) is how stairs and roofs are usually discussed. Percent grade is the convention for roads, ramps, and site drainage — a 5% ramp rises 5 units for every 100 of run. "1 in N" is common in plumbing falls and accessibility ramps (the ADA limit is 1 in 12). The diagonal is the true travel length along the slope, which is what you measure when ordering a stringer, handrail, or rafter. A quick sanity check: a 45-degree slope is exactly 100% grade and 1 in 1, because rise equals run. Anything steeper than 45 degrees passes 100%, which surprises people expecting percent to top out at 100. ## Finding a stair's angle The angle of a staircase is the arctangent of the rise over the run. For the slope of a single step (the true pitch a stringer is cut to) use the unit rise and unit tread; for the overall slope use total rise and total run. stair angle = atan(rise / run) × (180 / π) A 7.5-inch riser with a 10-inch tread gives atan(7.5 / 10) = 36.9 degrees. Most comfortable domestic stairs land between 30 and 38 degrees; codes cap the steepest stairs around 42 to 50 degrees depending on the standard. To size and check a full flight by angle, use the straight stair calculator . URL: https://staircalculators.net/calculators/ship-ladder/ Home / Calculators / Ship ladder calculator Calculator # Ship ladder calculator Steep ladder-stair geometry for tight spaces: run, rake, and step count at a chosen angle. This is a planning estimate only. Cantilever and curved stairs require engineered support; loads must be verified by a qualified engineer. Ship ladder calculator Total rise in Angle ° Target riser in Project name (for PDF) ✎ Ship ladder Results ↓ Download full PDF Steps — Riser — Run — Rake — ## Ship ladder geometry A ship ladder (or alternating-tread stair) is steeper than a normal stair, typically 50 to 75 degrees, for very tight spaces like lofts and mezzanines. It is not a code egress stair and usually requires a continuous handrail. run = rise / tan(angle) rake = rise / sin(angle) ## Frequently asked questions ### What angle is a ship ladder? Typically 50 to 75 degrees from horizontal, far steeper than a normal stair (30 to 38 degrees). ### Is a ship ladder code compliant as a stair? Generally no. Ship ladders are permitted only for limited access (lofts, mezzanines, equipment platforms), not as a required egress stair. ### What is an alternating tread stair? A very steep stair with treads shaped for left and right feet alternately, allowing a steeper pitch in minimal floor space. URL: https://staircalculators.net/calculators/skirt-board/ Home / Calculators / Skirt board calculator Calculator # Skirt board calculator Length of the skirt (skirting) board along the rake, plus the plumb and level cut angles at the ends. Skirt board calculator Total rise in Total run in Board width in Project name (for PDF) ✎ Skirt elevation Results ↓ Download full PDF Rake length — Plumb cut — Level cut — ## Skirt board layout The skirt board runs along the open or wall side of a stair, parallel to the stringer. Its length is the rake; the end cuts are a plumb (vertical) cut and a level (horizontal) cut set by the stair angle. rake = √(rise² + run²) plumb cut = stair angle ; level cut = 90° − angle ## Frequently asked questions ### What is a stair skirt board? A finish board that runs along the side of a staircase, covering the rough stringer and the joint where treads meet the wall. ### What angle do I cut a skirt board? The plumb (vertical) cut equals the stair angle from horizontal; the level (horizontal) cut is 90 degrees minus that angle. ### How long should a skirt board be? At least the diagonal rake length of the flight, plus a little for the end cuts. URL: https://staircalculators.net/calculators/spiral/ Home / Calculators / Spiral stair calculator Calculator 06 # Spiral stair calculator Helical stair geometry: arc tread depths at inner, walk-line and outer radii, clear width, rise per full turn, and outer handrail length. Spiral stair calculator Code IRC 2018 (US) IRC 2021 (US) IRC 2024 (US) IBC (US Commercial) UK Part K Eurocode (est.) AU NCC Total rise in Target riser in Outer diameter in Center column dia. in Total rotation ° Project name (for PDF) ✎ Plan — spiral Results ↓ Download full PDF Steps — Riser — Clear width — Walk arc — Rise/turn — Handrail — ## Helical geometry A spiral stair wraps treads around a center column. Each tread is an arc whose depth grows with radius, so the usable tread depth is measured along a walking line near the outer edge. Clear width is the outer radius minus the column radius. Rise per full turn determines headroom: a person on the stair must clear the underside of the flight one turn above. clear width = outer radius − column radius tread arc = radius × step angle (radians) handrail = √(outer arc total² + total rise²) Spiral codes differ widely — some jurisdictions allow steeper risers and narrower widths than straight stairs. Pending verification. URL: https://staircalculators.net/calculators/stair-lighting/ Home / Calculators / Stair lighting calculator Calculator # Stair lighting calculator Plan stair lighting: continuous LED strip length and LED count, or the number of per-step lights. Stair lighting calculator Number of steps Tread width in LEDs per foot /ft Lights per step Project name (for PDF) ✎ Lighting layout Results ↓ Download full PDF Strip length — LED count — Step lights — ## Stair lighting layout For a continuous look, a single LED strip runs under each tread nosing; total strip length is the step count times the tread width. For discrete step lights, multiply the step count by the lights per step. strip length = steps × tread width LED count = strip length (ft) × LEDs per foot ## Frequently asked questions ### How much LED strip do I need for stairs? Multiply the number of steps by the tread width to get the total run under the nosings. For 14 steps at 36 inches that is 504 inches, or 42 feet. ### How many step lights do I need? Usually one or two recessed lights per step, depending on tread width and how even you want the wash. Wider treads benefit from two. ### What LED density should I use for stairs? Common strip densities are 18, 30, or 60 LEDs per foot. Higher density gives a smoother line with no visible dots, useful close to the eye on open risers. URL: https://staircalculators.net/calculators/stair-opening/ Home / Calculators / Stair opening calculator Calculator # Stair opening calculator Size the floor opening your stair passes through so headroom is maintained all the way up. Stair opening calculator Building code IRC 2021 (US Residential) IRC 2018 IRC 2024 IBC (US Commercial) UK Part K Australia NCC Eurocode (estimate) Total rise in Total run in Target riser in Stair width in Floor assembly above in Project name (for PDF) ✎ Opening section Results ↓ Download full PDF Opening length — Opening width — Angle — Steps — ## Floor opening size The opening in the upper floor must be long enough that a climber clears the floor edge with full headroom, and wide enough to frame the stair with a small allowance each side. opening length = (floor assembly + min headroom) / tan(angle) ## Frequently asked questions ### How big should a stair floor opening be? Long enough to maintain the code headroom (80 inches under the IRC) as the climber passes the floor edge, and about 1 inch wider than the stair on each side for framing. ### What is a rough opening for stairs? The framed hole in the upper floor that the staircase rises through, sized before finishes. ### Why is my stair opening too short? A short opening pinches headroom at the top of the flight. Lengthen the opening or reduce the stair pitch. URL: https://staircalculators.net/calculators/stair-tread/ Home / Stair tread calculator Calculator 01 # Stair tread calculator Calculate tread depth, total tread count, and whether your tread meets code — the horizontal dimension that controls stair comfort and compliance. Straight Stair Code IRC 2018 (US) IRC 2021 (US) IRC 2024 (US) IBC (US Commercial) UK Part K Eurocode (est.) AU NCC Total rise in Total run (avail.) in Target riser in Stair width in Project name (for PDF) ✎ Elevation — side view — Results ↓ Download full PDF Steps — Riser — Tread — Stringer — Angle — 2R+T — ## Tread depth and count The tread is the horizontal part of a step you walk on; its depth (the "going") is one of the two numbers that define a stair. This calculator focuses on the tread, using the same engine as the straight stair calculator . ## Frequently asked questions ### What is the minimum stair tread depth? The IRC requires 10 inches; the IBC commercial standard 11 inches; the Australian NCC 240 mm. ### How many treads are in a staircase? Always one fewer than the number of risers. ### What is the difference between tread depth and going? They are the same horizontal dimension; "going" is the British/Australian term. URL: https://staircalculators.net/calculators/steel-stair/ Home / Calculators / Steel stair calculator Calculator # Steel stair calculator Estimate the steel weight of stair stringers from the rake length and the section weight per foot. Steel weights are nominal estimates from the section weight you enter. Confirm member sizes and connections with a structural engineer. Steel stair calculator Total rise in Total run in Stringers Section lb/ft lb/ft Project name (for PDF) ✎ Steel stringer Results ↓ Download full PDF Rake length — Rake (ft) — Steel weight — ## Steel stringer weight For a steel stair, a quick weight estimate comes from the rake length times the section weight per foot times the number of stringers. Enter the channel or plate weight per foot from the supplier table. weight = rake(ft) × lb/ft × stringers ## Frequently asked questions ### How do I estimate steel stair weight? Multiply the stringer rake length in feet by the section weight per foot, then by the number of stringers. Add treads, landings, and connections separately. ### What steel section is used for stair stringers? Commonly channels (C or MC shapes) or bent plate. The weight per foot comes from the steel supplier table for the chosen section. ### Is this a structural design? No. It is a weight estimate only. A structural engineer must size the members and connections. URL: https://staircalculators.net/calculators/straight-stair/ Home / Calculators / Straight stair Calculator 01 # Straight stair calculator Enter total rise and available run. Get riser, tread, stringer length and angle, a live code check, and a complete build packet PDF. Straight Stair Code IRC 2018 (US) IRC 2021 (US) IRC 2024 (US) IBC (US Commercial) UK Part K Eurocode (est.) AU NCC Total rise in Total run (avail.) in Target riser in Stair width in Project name (for PDF) ✎ Elevation — side view — Results ↓ Download full PDF Steps — Riser — Tread — Stringer — Angle — 2R+T — ## How the straight stair calculation works The step count is the total rise divided by your target riser height, rounded to the nearest whole step. Dividing total rise by that step count gives the actual riser height, kept equal across every step as code requires. Tread depth is the available run divided by the number of treads, which is one less than the step count because the top step lands on the floor above. stringer length = √(total rise² + total run²) angle = atan(total rise / total run) comfort (Blondel) = 2 × riser + tread ≈ 24–25 in Compliance thresholds shown here are being finalized against primary code sources. Always confirm against the building code edition enforced by your local authority having jurisdiction before cutting or pouring. ## Reading the code check Pick your jurisdiction in the calculator header. Each result re-checks live against that code's riser, tread and width limits, with the governing clause shown beside every line. Switching between editions — IRC 2021 and 2024, for example — recalculates instantly. URL: https://staircalculators.net/calculators/stringer/ Home / Calculators / Stair stringer calculator Calculator # Stair stringer calculator Size the notched board that carries your steps: cut length, throat depth behind each notch, and the right board (2x10 vs 2x12). Stair stringer calculator Building code IRC 2021 (US Residential) IRC 2018 IRC 2024 IBC (US Commercial) UK Part K Australia NCC Eurocode (estimate) Total rise in Total run in Target riser in Tread depth in Project name (for PDF) ✎ Stringer elevation Results ↓ Download full PDF Length — Board — Throat2x12 — Angle — Steps — ## Stringer length and throat The stringer is the sloped board the steps are cut from. Its length is the hypotenuse of the rise and run; the throat is the sound wood remaining behind each notch, which must stay at least 3.5 inches for a cut stringer. This calculator gives both, recommends a board size, and rounds up to a standard purchase length. stringer = √(rise² + run²) throat = board depth − (riser × tread / notch hypotenuse) ## Frequently asked questions ### What size board do I need for stair stringers? A cut stringer must keep at least 3.5 inches of sound wood behind each notch. Most residential step geometry needs a 2x12; a 2x10 only works for shallow steps. ### How long should my stringer board be? At least the diagonal length (square root of rise squared plus run squared), plus 6 to 12 inches for the top and bottom cuts. Buy the next standard board length up. ### What is stringer throat depth? The perpendicular distance of sound wood behind a notch. It equals the board depth minus the notch triangle perpendicular height (riser times tread divided by the notch hypotenuse). URL: https://staircalculators.net/calculators/switchback/ Home / Calculators / Switchback stair calculator Calculator 04 # Switchback stair calculator A switchback stair reverses 180° with two parallel flights and an intermediate landing. Common in commercial and exterior settings. U-shape stair calculator Code IRC 2018 (US) IRC 2021 (US) IRC 2024 (US) IBC (US Commercial) UK Part K Eurocode (est.) AU NCC Total rise in Target riser in Tread depth in Stair width in Well gap in Project name (for PDF) ✎ Plan — half turn Results ↓ Download full PDF Steps — Riser — Lower flight — Upper flight — Footprint X — Footprint Y — ## What is a switchback stair? A switchback (or scissor) stair runs up one flight, turns 180 degrees at a landing, and continues up a parallel flight in the opposite direction. Structurally it is identical to a U-shaped / half-turn stair ; "switchback" is the term favoured for commercial egress and exterior hillside stairs. ## Frequently asked questions ### Is a switchback stair the same as a U-shaped stair? Yes, structurally. A switchback reverses direction 180 degrees with parallel flights. ### Where are switchback stairs used? Commercial egress stairwells, parking structures, and hillside or landscape stairs. ### Do switchback stairs need a landing? Yes. The 180° reversal happens at an intermediate landing. URL: https://staircalculators.net/calculators/timber-estimator/ Home / Calculators / Timber estimator (board feet) Calculator # Timber estimator (board feet) Estimate the board feet of lumber for stair components from the piece dimensions and count. Timber estimator (board feet) Thickness in Width in Length in Pieces Project name (for PDF) ✎ Board Results ↓ Download full PDF Board feet each — Board feet total — Length — ## Board feet A board foot is a volume of lumber 1 inch thick, 12 inches wide, and 12 inches long (144 cubic inches). Lumber is often priced per board foot, so this converts your piece dimensions into board feet for ordering and budgeting. board feet = (thickness × width × length in inches) / 144 ## Frequently asked questions ### What is a board foot? A unit of lumber volume equal to a board 1 inch thick, 12 inches wide, and 1 foot long, or 144 cubic inches. ### How do I calculate board feet? Multiply thickness by width by length in inches, then divide by 144. Multiply by the number of pieces for the total. ### Should I use nominal or actual lumber size? Use actual dimensions for an accurate volume (a 2x12 is actually 1.5 by 11.25 inches). Suppliers may price on nominal size, so check how your yard quotes. URL: https://staircalculators.net/calculators/u-shape/ Home / Calculators / U-shape stair calculator Calculator 04 # U-shape stair calculator Half-turn switchback stairs: solve the flight split, half-landing, and the stairwell footprint including the well gap. U-shape stair calculator Code IRC 2018 (US) IRC 2021 (US) IRC 2024 (US) IBC (US Commercial) UK Part K Eurocode (est.) AU NCC Total rise in Target riser in Tread depth in Stair width in Well gap in Project name (for PDF) ✎ Plan — half turn Results ↓ Download full PDF Steps — Riser — Lower flight — Upper flight — Footprint X — Footprint Y — ## The half-turn switchback A U-shape stair doubles back 180 degrees around a half-landing. Both flights run parallel, so the stairwell width is two stair widths plus the well gap between them. This is the most compact footprint for a given rise, which is why switchbacks are common in tight stairwells. Compliance thresholds pending verification. ## How a U-shaped stair is sized A U-shaped (half-turn) stair doubles back 180 degrees around a central landing, stacking two parallel flights side by side. It is the most compact way to climb a full storey, which is why it is common in stairwells and multi-storey homes where floor area is tight. The calculator splits your total rise into uniform risers across both flights and sizes the landing that joins them. The landing is the key dimension: it must be at least as deep, in the direction of travel, as the stair is wide, and never less than 36 inches under the IRC. Because a U-shape turns at the landing rather than with pie-shaped winder treads, it is easier to build and more forgiving to climb than a winder of the same turn — the trade-off is the floor area the landing consumes. URL: https://staircalculators.net/calculators/winder/ Home / Calculators / Winder stair calculator Calculator 05 # Winder stair calculator Pie-shaped winder treads done right: narrow-end depth, walking-line depth (measured from the narrow end), and per-tread code checks. Winder stair calculator Code IRC 2018 (US) IRC 2021 (US) IRC 2024 (US) IBC (US Commercial) UK Part K Eurocode (est.) AU NCC Total rise in Target riser in Inner radius (newel) in Stair width in Turn angle ° Winder treads # Project name (for PDF) ✎ Plan — winder treads Results ↓ Download full PDF Steps — Riser — Step angle — Narrow depth — Walk-line depth — Wide depth — ## Why winders fail inspection Winder treads are pie-shaped: narrow at the inside of the turn, wide at the outside. Codes set a minimum depth at the narrow end and a minimum depth along the walking line, which is measured a fixed distance from the narrow side. Each winder tread is an arc, so its depth is the radius at that point multiplied by the angle the tread sweeps. tread depth = radius × step angle (radians) walk line measured the code-specified offset from the narrow end (varies by code) A tight inner radius or too many treads in the turn shrinks the narrow end below the minimum — the most common winder failure. Adjust the inner radius, turn angle, or winder count until both checks pass. Winder thresholds vary significantly by jurisdiction. Pending primary-source verification. ============================================================ RISER & TREAD COMBINATIONS ============================================================ URL: https://staircalculators.net/combinations/6-5x11/ Home / Combinations / 6.5″ × 11″ Rise × run # 6.5″ rise × 11″ run stairs What a 6.5-inch riser paired with a 11-inch tread actually gives you — pitch, comfort, and code status — plus the calculator to size a full flight. Pitch 30.6 ° Blondel 2R+T 24.0 in Comfort Ideal ## Code status A 6.5-inch riser with a 11-inch tread is compliant under IRC 2021 (max riser 7.75″, min tread 10.0″), and compliant under the IBC commercial standard (max riser 7.0″, min tread 11.0″). ## The numbers pitch = atan(6.5 / 11) = 30.6° Blondel = 2 × 6.5 + 11 = 24.0″ (ideal ≈ 24–25) This pair is one step's geometry. To size a complete flight for your floor-to-floor height, enter your total rise in the calculator and it will hold the riser near 6.5″ while checking every code limit. Size a full flight ## What this combination is like to use A 6.5-inch riser with a 11-inch tread produces a 30.6-degree pitch, which is one of the more relaxed pairings for a staircase. In practice that means it is easy to climb and descend, friendly for children and older users, but it consumes the most horizontal run. Its Blondel value of 24.0 inches lands right in the 24–25 inch Blondel comfort band, so it should feel natural underfoot. Across a typical flight of about 14 treads, the 11-inch tread depth works out to roughly 11.9 feet of horizontal run — a moderate footprint. This pairing clears both the residential IRC and the stricter commercial IBC, which makes it unusually versatile — usable in a home or a light-commercial setting without redesign. ## When to choose it Pick this pairing when comfort and easy access matter more than saving floor area — it is a good main-stair choice in a home with the space to accommodate the longer run. Whatever your floor-to-floor height, the calculator below will hold the riser near 6.5 inches, divide the rise into uniform steps, and check the result against the code you select. ## Nearby combinations 7.5″ × 11″ , 7.75″ × 10″ , 7″ × 10.5″ , 7.25″ × 10.5″ URL: https://staircalculators.net/combinations/6-75x11/ Home / Combinations / 6.75″ × 11″ Rise × run # 6.75″ rise × 11″ run stairs What a 6.75-inch riser paired with a 11-inch tread actually gives you — pitch, comfort, and code status — plus the calculator to size a full flight. Pitch 31.5 ° Blondel 2R+T 24.5 in Comfort Ideal ## Code status A 6.75-inch riser with a 11-inch tread is compliant under IRC 2021 (max riser 7.75″, min tread 10.0″), and compliant under the IBC commercial standard (max riser 7.0″, min tread 11.0″). ## The numbers pitch = atan(6.75 / 11) = 31.5° Blondel = 2 × 6.75 + 11 = 24.5″ (ideal ≈ 24–25) This pair is one step's geometry. To size a complete flight for your floor-to-floor height, enter your total rise in the calculator and it will hold the riser near 6.75″ while checking every code limit. Size a full flight ## What this combination is like to use A 6.75-inch riser with a 11-inch tread produces a 31.5-degree pitch, which is squarely in the comfortable range for a staircase. In practice that means it is a natural everyday rhythm that suits a main staircase. Its Blondel value of 24.5 inches lands right in the 24–25 inch Blondel comfort band, so it should feel natural underfoot. Across a typical flight of about 14 treads, the 11-inch tread depth works out to roughly 11.9 feet of horizontal run — a moderate footprint. This pairing clears both the residential IRC and the stricter commercial IBC, which makes it unusually versatile — usable in a home or a light-commercial setting without redesign. ## When to choose it Pick this pairing when comfort and easy access matter more than saving floor area — it is a good main-stair choice in a home with the space to accommodate the longer run. Whatever your floor-to-floor height, the calculator below will hold the riser near 6.75 inches, divide the rise into uniform steps, and check the result against the code you select. ## Nearby combinations 8.25″ × 9″ , 7.5″ × 9.5″ , 7.5″ × 10.5″ URL: https://staircalculators.net/combinations/6x12/ Home / Combinations / 6″ × 12″ Rise × run # 6″ rise × 12″ run stairs What a 6-inch riser paired with a 12-inch tread actually gives you — pitch, comfort, and code status — plus the calculator to size a full flight. Pitch 26.6 ° Blondel 2R+T 24 in Comfort Ideal ## Code status A 6-inch riser with a 12-inch tread is compliant under IRC 2021 (max riser 7.75″, min tread 10.0″), and compliant under the IBC commercial standard (max riser 7.0″, min tread 11.0″). ## The numbers pitch = atan(6 / 12) = 26.6° Blondel = 2 × 6 + 12 = 24″ (ideal ≈ 24–25) This pair is one step's geometry. To size a complete flight for your floor-to-floor height, enter your total rise in the calculator and it will hold the riser near 6″ while checking every code limit. Size a full flight ## What this combination is like to use A 6-inch riser with a 12-inch tread produces a 26.6-degree pitch, which is one of the more relaxed pairings for a staircase. In practice that means it is easy to climb and descend, friendly for children and older users, but it consumes the most horizontal run. Its Blondel value of 24.0 inches lands right in the 24–25 inch Blondel comfort band, so it should feel natural underfoot. Across a typical flight of about 14 treads, the 12-inch tread depth works out to roughly 13.0 feet of horizontal run — a generous footprint that needs more floor space. This pairing clears both the residential IRC and the stricter commercial IBC, which makes it unusually versatile — usable in a home or a light-commercial setting without redesign. ## When to choose it Pick this pairing when comfort and easy access matter more than saving floor area — it is a good main-stair choice in a home with the space to accommodate the longer run. Whatever your floor-to-floor height, the calculator below will hold the riser near 6 inches, divide the rise into uniform steps, and check the result against the code you select. ## Nearby combinations 8″ × 9″ , 7″ × 12″ , 7.25″ × 10.5″ , 7.5″ × 10.5″ URL: https://staircalculators.net/combinations/7-25x10-5/ Home / Combinations / 7.25″ × 10.5″ Rise × run # 7.25″ rise × 10.5″ run stairs What a 7.25-inch riser paired with a 10.5-inch tread actually gives you — pitch, comfort, and code status — plus the calculator to size a full flight. Pitch 34.6 ° Blondel 2R+T 25.0 in Comfort Ideal ## Code status A 7.25-inch riser with a 10.5-inch tread is compliant under IRC 2021 (max riser 7.75″, min tread 10.0″), and non-compliant under the IBC commercial standard (max riser 7.0″, min tread 11.0″). ## The numbers pitch = atan(7.25 / 10.5) = 34.6° Blondel = 2 × 7.25 + 10.5 = 25.0″ (ideal ≈ 24–25) This pair is one step's geometry. To size a complete flight for your floor-to-floor height, enter your total rise in the calculator and it will hold the riser near 7.25″ while checking every code limit. Size a full flight ## What this combination is like to use A 7.25-inch riser with a 10.5-inch tread produces a 34.6-degree pitch, which is squarely in the comfortable range for a staircase. In practice that means it is a natural everyday rhythm that suits a main staircase. Its Blondel value of 25.0 inches lands right in the 24–25 inch Blondel comfort band, so it should feel natural underfoot. Across a typical flight of about 14 treads, the 10.5-inch tread depth works out to roughly 11.4 feet of horizontal run — a moderate footprint. It is fine for a residential stair under the IRC but would fail an IBC commercial plan review because its 7.25-inch riser exceeds the IBC's 7-inch cap and its 10.5-inch tread is below the IBC's 11-inch minimum. ## When to choose it This is a sound general-purpose main-stair pairing: comfortable to climb yet reasonably efficient with floor space. Whatever your floor-to-floor height, the calculator below will hold the riser near 7.25 inches, divide the rise into uniform steps, and check the result against the code you select. ## Nearby combinations 7.75″ × 10″ , 8″ × 9″ , 6.5″ × 11″ , 6″ × 12″ URL: https://staircalculators.net/combinations/7-5x10-5/ Home / Combinations / 7.5″ × 10.5″ Rise × run # 7.5″ rise × 10.5″ run stairs What a 7.5-inch riser paired with a 10.5-inch tread actually gives you — pitch, comfort, and code status — plus the calculator to size a full flight. Pitch 35.5 ° Blondel 2R+T 25.5 in Comfort Ideal ## Code status A 7.5-inch riser with a 10.5-inch tread is compliant under IRC 2021 (max riser 7.75″, min tread 10.0″), and non-compliant under the IBC commercial standard (max riser 7.0″, min tread 11.0″). ## The numbers pitch = atan(7.5 / 10.5) = 35.5° Blondel = 2 × 7.5 + 10.5 = 25.5″ (ideal ≈ 24–25) This pair is one step's geometry. To size a complete flight for your floor-to-floor height, enter your total rise in the calculator and it will hold the riser near 7.5″ while checking every code limit. Size a full flight ## What this combination is like to use A 7.5-inch riser with a 10.5-inch tread produces a 35.5-degree pitch, which is on the brisk side of comfortable for a staircase. In practice that means it is efficient with floor space while staying easy to use. Its Blondel value of 25.5 inches sits just above the 24–25 inch Blondel band — a touch tall in the step, but still comfortable. Across a typical flight of about 14 treads, the 10.5-inch tread depth works out to roughly 11.4 feet of horizontal run — a moderate footprint. It is fine for a residential stair under the IRC but would fail an IBC commercial plan review because its 7.5-inch riser exceeds the IBC's 7-inch cap and its 10.5-inch tread is below the IBC's 11-inch minimum. ## When to choose it This is a sound general-purpose main-stair pairing: comfortable to climb yet reasonably efficient with floor space. Whatever your floor-to-floor height, the calculator below will hold the riser near 7.5 inches, divide the rise into uniform steps, and check the result against the code you select. ## Nearby combinations 7″ × 12″ , 8.25″ × 9″ , 6″ × 12″ , 6.75″ × 11″ URL: https://staircalculators.net/combinations/7-5x10/ Home / Combinations / 7.5″ × 10″ Rise × run # 7.5″ rise × 10″ run stairs What a 7.5-inch riser paired with a 10-inch tread actually gives you — pitch, comfort, and code status — plus the calculator to size a full flight. Pitch 36.9 ° Blondel 2R+T 25.0 in Comfort Ideal ## Code status A 7.5-inch riser with a 10-inch tread is compliant under IRC 2021 (max riser 7.75″, min tread 10.0″), and non-compliant under the IBC commercial standard (max riser 7.0″, min tread 11.0″). ## The numbers pitch = atan(7.5 / 10) = 36.9° Blondel = 2 × 7.5 + 10 = 25.0″ (ideal ≈ 24–25) This pair is one step's geometry. To size a complete flight for your floor-to-floor height, enter your total rise in the calculator and it will hold the riser near 7.5″ while checking every code limit. Size a full flight ## What this combination is like to use A 7.5-inch riser with a 10-inch tread produces a 36.9-degree pitch, which is on the brisk side of comfortable for a staircase. In practice that means it is efficient with floor space while staying easy to use. Its Blondel value of 25.0 inches lands right in the 24–25 inch Blondel comfort band, so it should feel natural underfoot. Across a typical flight of about 14 treads, the 10-inch tread depth works out to roughly 10.8 feet of horizontal run — a compact footprint. It is fine for a residential stair under the IRC but would fail an IBC commercial plan review because its 7.5-inch riser exceeds the IBC's 7-inch cap and its 10-inch tread is below the IBC's 11-inch minimum. ## When to choose it This is a sound general-purpose main-stair pairing: comfortable to climb yet reasonably efficient with floor space. Whatever your floor-to-floor height, the calculator below will hold the riser near 7.5 inches, divide the rise into uniform steps, and check the result against the code you select. ## Nearby combinations 7″ × 10″ , 7″ × 10.5″ , 7″ × 11″ , 7.5″ × 11″ URL: https://staircalculators.net/combinations/7-5x11/ Home / Combinations / 7.5″ × 11″ Rise × run # 7.5″ rise × 11″ run stairs What a 7.5-inch riser paired with a 11-inch tread actually gives you — pitch, comfort, and code status — plus the calculator to size a full flight. Pitch 34.3 ° Blondel 2R+T 26.0 in Comfort Outside ## Code status A 7.5-inch riser with a 11-inch tread is compliant under IRC 2021 (max riser 7.75″, min tread 10.0″), and non-compliant under the IBC commercial standard (max riser 7.0″, min tread 11.0″). ## The numbers pitch = atan(7.5 / 11) = 34.3° Blondel = 2 × 7.5 + 11 = 26.0″ (ideal ≈ 24–25) This pair is one step's geometry. To size a complete flight for your floor-to-floor height, enter your total rise in the calculator and it will hold the riser near 7.5″ while checking every code limit. Size a full flight ## What this combination is like to use A 7.5-inch riser with a 11-inch tread produces a 34.3-degree pitch, which is squarely in the comfortable range for a staircase. In practice that means it is a natural everyday rhythm that suits a main staircase. Its Blondel value of 26.0 inches sits just above the 24–25 inch Blondel band — a touch tall in the step, but still comfortable. Across a typical flight of about 14 treads, the 11-inch tread depth works out to roughly 11.9 feet of horizontal run — a moderate footprint. It is fine for a residential stair under the IRC but would fail an IBC commercial plan review because its 7.5-inch riser exceeds the IBC's 7-inch cap. ## When to choose it This is a sound general-purpose main-stair pairing: comfortable to climb yet reasonably efficient with floor space. Whatever your floor-to-floor height, the calculator below will hold the riser near 7.5 inches, divide the rise into uniform steps, and check the result against the code you select. ## Nearby combinations 7″ × 10.5″ , 6.5″ × 11″ , 7.5″ × 10″ , 7.75″ × 10″ URL: https://staircalculators.net/combinations/7-5x9-5/ Home / Combinations / 7.5″ × 9.5″ Rise × run # 7.5″ rise × 9.5″ run stairs What a 7.5-inch riser paired with a 9.5-inch tread actually gives you — pitch, comfort, and code status — plus the calculator to size a full flight. Pitch 38.3 ° Blondel 2R+T 24.5 in Comfort Ideal ## Code status A 7.5-inch riser with a 9.5-inch tread is non-compliant under IRC 2021 (max riser 7.75″, min tread 10.0″), and non-compliant under the IBC commercial standard (max riser 7.0″, min tread 11.0″). ## The numbers pitch = atan(7.5 / 9.5) = 38.3° Blondel = 2 × 7.5 + 9.5 = 24.5″ (ideal ≈ 24–25) This pair is one step's geometry. To size a complete flight for your floor-to-floor height, enter your total rise in the calculator and it will hold the riser near 7.5″ while checking every code limit. Size a full flight ## What this combination is like to use A 7.5-inch riser with a 9.5-inch tread produces a 38.3-degree pitch, which is near the steep end of what is normally built for a staircase. In practice that means it is space-saving but tiring on a long climb and demanding on the way down. Its Blondel value of 24.5 inches lands right in the 24–25 inch Blondel comfort band, so it should feel natural underfoot. Across a typical flight of about 14 treads, the 9.5-inch tread depth works out to roughly 10.3 feet of horizontal run — a compact footprint. Note that this pairing does not meet the residential IRC because the 9.5-inch tread is under the IRC's 10-inch minimum, so it would need adjustment before use in a typical home. ## When to choose it Reach for this pairing when floor space is tight and a steeper, more compact stair is acceptable — for example a secondary, basement, or loft stair rather than the primary staircase. Whatever your floor-to-floor height, the calculator below will hold the riser near 7.5 inches, divide the rise into uniform steps, and check the result against the code you select. ## Nearby combinations 6.75″ × 11″ , 8.25″ × 9″ URL: https://staircalculators.net/combinations/7-75x10/ Home / Combinations / 7.75″ × 10″ Rise × run # 7.75″ rise × 10″ run stairs What a 7.75-inch riser paired with a 10-inch tread actually gives you — pitch, comfort, and code status — plus the calculator to size a full flight. Pitch 37.8 ° Blondel 2R+T 25.5 in Comfort Ideal ## Code status A 7.75-inch riser with a 10-inch tread is compliant under IRC 2021 (max riser 7.75″, min tread 10.0″), and non-compliant under the IBC commercial standard (max riser 7.0″, min tread 11.0″). ## The numbers pitch = atan(7.75 / 10) = 37.8° Blondel = 2 × 7.75 + 10 = 25.5″ (ideal ≈ 24–25) This pair is one step's geometry. To size a complete flight for your floor-to-floor height, enter your total rise in the calculator and it will hold the riser near 7.75″ while checking every code limit. Size a full flight ## What this combination is like to use A 7.75-inch riser with a 10-inch tread produces a 37.8-degree pitch, which is on the brisk side of comfortable for a staircase. In practice that means it is efficient with floor space while staying easy to use. Its Blondel value of 25.5 inches sits just above the 24–25 inch Blondel band — a touch tall in the step, but still comfortable. Across a typical flight of about 14 treads, the 10-inch tread depth works out to roughly 10.8 feet of horizontal run — a compact footprint. It is fine for a residential stair under the IRC but would fail an IBC commercial plan review because its 7.75-inch riser exceeds the IBC's 7-inch cap and its 10-inch tread is below the IBC's 11-inch minimum. ## When to choose it This is a sound general-purpose main-stair pairing: comfortable to climb yet reasonably efficient with floor space. Whatever your floor-to-floor height, the calculator below will hold the riser near 7.75 inches, divide the rise into uniform steps, and check the result against the code you select. ## Nearby combinations 6.5″ × 11″ , 7.25″ × 10.5″ , 7.5″ × 11″ , 8″ × 9″ URL: https://staircalculators.net/combinations/7x10-5/ Home / Combinations / 7″ × 10.5″ Rise × run # 7″ rise × 10.5″ run stairs What a 7-inch riser paired with a 10.5-inch tread actually gives you — pitch, comfort, and code status — plus the calculator to size a full flight. Pitch 33.7 ° Blondel 2R+T 24.5 in Comfort Ideal ## Code status A 7-inch riser with a 10.5-inch tread is compliant under IRC 2021 (max riser 7.75″, min tread 10.0″), and non-compliant under the IBC commercial standard (max riser 7.0″, min tread 11.0″). ## The numbers pitch = atan(7 / 10.5) = 33.7° Blondel = 2 × 7 + 10.5 = 24.5″ (ideal ≈ 24–25) This pair is one step's geometry. To size a complete flight for your floor-to-floor height, enter your total rise in the calculator and it will hold the riser near 7″ while checking every code limit. Size a full flight ## What this combination is like to use A 7-inch riser with a 10.5-inch tread produces a 33.7-degree pitch, which is squarely in the comfortable range for a staircase. In practice that means it is a natural everyday rhythm that suits a main staircase. Its Blondel value of 24.5 inches lands right in the 24–25 inch Blondel comfort band, so it should feel natural underfoot. Across a typical flight of about 14 treads, the 10.5-inch tread depth works out to roughly 11.4 feet of horizontal run — a moderate footprint. It is fine for a residential stair under the IRC but would fail an IBC commercial plan review because its 10.5-inch tread is below the IBC's 11-inch minimum. ## When to choose it Pick this pairing when comfort and easy access matter more than saving floor area — it is a good main-stair choice in a home with the space to accommodate the longer run. Whatever your floor-to-floor height, the calculator below will hold the riser near 7 inches, divide the rise into uniform steps, and check the result against the code you select. ## Nearby combinations 7.5″ × 10″ , 7.5″ × 11″ , 7″ × 10″ , 6.5″ × 11″ URL: https://staircalculators.net/combinations/7x10/ Home / Combinations / 7″ × 10″ Rise × run # 7″ rise × 10″ run stairs What a 7-inch riser paired with a 10-inch tread actually gives you — pitch, comfort, and code status — plus the calculator to size a full flight. Pitch 35.0 ° Blondel 2R+T 24 in Comfort Ideal ## Code status A 7-inch riser with a 10-inch tread is compliant under IRC 2021 (max riser 7.75″, min tread 10.0″), and non-compliant under the IBC commercial standard (max riser 7.0″, min tread 11.0″). ## The numbers pitch = atan(7 / 10) = 35.0° Blondel = 2 × 7 + 10 = 24″ (ideal ≈ 24–25) This pair is one step's geometry. To size a complete flight for your floor-to-floor height, enter your total rise in the calculator and it will hold the riser near 7″ while checking every code limit. Size a full flight ## What this combination is like to use A 7-inch riser with a 10-inch tread produces a 35.0-degree pitch, which is on the brisk side of comfortable for a staircase. In practice that means it is efficient with floor space while staying easy to use. Its Blondel value of 24.0 inches lands right in the 24–25 inch Blondel comfort band, so it should feel natural underfoot. Across a typical flight of about 14 treads, the 10-inch tread depth works out to roughly 10.8 feet of horizontal run — a compact footprint. It is fine for a residential stair under the IRC but would fail an IBC commercial plan review because its 10-inch tread is below the IBC's 11-inch minimum. ## When to choose it This is a sound general-purpose main-stair pairing: comfortable to climb yet reasonably efficient with floor space. Whatever your floor-to-floor height, the calculator below will hold the riser near 7 inches, divide the rise into uniform steps, and check the result against the code you select. ## Nearby combinations 7″ × 11″ , 7.5″ × 10″ , 7″ × 10.5″ URL: https://staircalculators.net/combinations/7x11/ Home / Combinations / 7″ × 11″ Rise × run # 7″ rise × 11″ run stairs What a 7-inch riser paired with a 11-inch tread actually gives you — pitch, comfort, and code status — plus the calculator to size a full flight. Pitch 32.5 ° Blondel 2R+T 25 in Comfort Ideal ## Code status A 7-inch riser with a 11-inch tread is compliant under IRC 2021 (max riser 7.75″, min tread 10.0″), and compliant under the IBC commercial standard (max riser 7.0″, min tread 11.0″). ## The numbers pitch = atan(7 / 11) = 32.5° Blondel = 2 × 7 + 11 = 25″ (ideal ≈ 24–25) This pair is one step's geometry. To size a complete flight for your floor-to-floor height, enter your total rise in the calculator and it will hold the riser near 7″ while checking every code limit. Size a full flight ## What this combination is like to use A 7-inch riser with a 11-inch tread produces a 32.5-degree pitch, which is squarely in the comfortable range for a staircase. In practice that means it is a natural everyday rhythm that suits a main staircase. Its Blondel value of 25.0 inches lands right in the 24–25 inch Blondel comfort band, so it should feel natural underfoot. Across a typical flight of about 14 treads, the 11-inch tread depth works out to roughly 11.9 feet of horizontal run — a moderate footprint. This pairing clears both the residential IRC and the stricter commercial IBC, which makes it unusually versatile — usable in a home or a light-commercial setting without redesign. ## When to choose it Pick this pairing when comfort and easy access matter more than saving floor area — it is a good main-stair choice in a home with the space to accommodate the longer run. Whatever your floor-to-floor height, the calculator below will hold the riser near 7 inches, divide the rise into uniform steps, and check the result against the code you select. ## Nearby combinations 7″ × 10″ , 7.5″ × 10″ URL: https://staircalculators.net/combinations/7x12/ Home / Combinations / 7″ × 12″ Rise × run # 7″ rise × 12″ run stairs What a 7-inch riser paired with a 12-inch tread actually gives you — pitch, comfort, and code status — plus the calculator to size a full flight. Pitch 30.3 ° Blondel 2R+T 26 in Comfort Outside ## Code status A 7-inch riser with a 12-inch tread is compliant under IRC 2021 (max riser 7.75″, min tread 10.0″), and compliant under the IBC commercial standard (max riser 7.0″, min tread 11.0″). ## The numbers pitch = atan(7 / 12) = 30.3° Blondel = 2 × 7 + 12 = 26″ (ideal ≈ 24–25) This pair is one step's geometry. To size a complete flight for your floor-to-floor height, enter your total rise in the calculator and it will hold the riser near 7″ while checking every code limit. Size a full flight ## What this combination is like to use A 7-inch riser with a 12-inch tread produces a 30.3-degree pitch, which is one of the more relaxed pairings for a staircase. In practice that means it is easy to climb and descend, friendly for children and older users, but it consumes the most horizontal run. Its Blondel value of 26.0 inches sits just above the 24–25 inch Blondel band — a touch tall in the step, but still comfortable. Across a typical flight of about 14 treads, the 12-inch tread depth works out to roughly 13.0 feet of horizontal run — a generous footprint that needs more floor space. This pairing clears both the residential IRC and the stricter commercial IBC, which makes it unusually versatile — usable in a home or a light-commercial setting without redesign. ## When to choose it Pick this pairing when comfort and easy access matter more than saving floor area — it is a good main-stair choice in a home with the space to accommodate the longer run. Whatever your floor-to-floor height, the calculator below will hold the riser near 7 inches, divide the rise into uniform steps, and check the result against the code you select. ## Nearby combinations 6″ × 12″ , 7.5″ × 10.5″ , 8″ × 9″ , 8.25″ × 9″ URL: https://staircalculators.net/combinations/8-25x9/ Home / Combinations / 8.25″ × 9″ Rise × run # 8.25″ rise × 9″ run stairs What a 8.25-inch riser paired with a 9-inch tread actually gives you — pitch, comfort, and code status — plus the calculator to size a full flight. Pitch 42.5 ° Blondel 2R+T 25.5 in Comfort Ideal ## Code status An 8.25-inch riser with a 9-inch tread is non-compliant under IRC 2021 (max riser 7.75″, min tread 10.0″), and non-compliant under the IBC commercial standard (max riser 7.0″, min tread 11.0″). ## The numbers pitch = atan(8.25 / 9) = 42.5° Blondel = 2 × 8.25 + 9 = 25.5″ (ideal ≈ 24–25) This pair is one step's geometry. To size a complete flight for your floor-to-floor height, enter your total rise in the calculator and it will hold the riser near 8.25″ while checking every code limit. Size a full flight ## What this combination is like to use An 8.25-inch riser with a 9-inch tread produces a 42.5-degree pitch, which is at the upper limit of buildable residential pitch for a staircase. In practice that means it is strictly space-saving and best reserved for secondary access. Its Blondel value of 25.5 inches sits just above the 24–25 inch Blondel band — a touch tall in the step, but still comfortable. Across a typical flight of about 14 treads, the 9-inch tread depth works out to roughly 9.8 feet of horizontal run — a compact footprint. Note that this pairing does not meet the residential IRC because the 8.25-inch riser exceeds the IRC's 7.75-inch maximum and the 9-inch tread is under the IRC's 10-inch minimum, so it would need adjustment before use in a typical home. ## When to choose it Reach for this pairing when floor space is tight and a steeper, more compact stair is acceptable — for example a secondary, basement, or loft stair rather than the primary staircase. Whatever your floor-to-floor height, the calculator below will hold the riser near 8.25 inches, divide the rise into uniform steps, and check the result against the code you select. ## Nearby combinations 7.5″ × 10.5″ , 6.75″ × 11″ , 7″ × 12″ , 7.5″ × 9.5″ URL: https://staircalculators.net/combinations/8x9/ Home / Combinations / 8″ × 9″ Rise × run # 8″ rise × 9″ run stairs What a 8-inch riser paired with a 9-inch tread actually gives you — pitch, comfort, and code status — plus the calculator to size a full flight. Pitch 41.6 ° Blondel 2R+T 25 in Comfort Ideal ## Code status An 8-inch riser with a 9-inch tread is non-compliant under IRC 2021 (max riser 7.75″, min tread 10.0″), and non-compliant under the IBC commercial standard (max riser 7.0″, min tread 11.0″). ## The numbers pitch = atan(8 / 9) = 41.6° Blondel = 2 × 8 + 9 = 25″ (ideal ≈ 24–25) This pair is one step's geometry. To size a complete flight for your floor-to-floor height, enter your total rise in the calculator and it will hold the riser near 8″ while checking every code limit. Size a full flight ## What this combination is like to use An 8-inch riser with a 9-inch tread produces a 41.6-degree pitch, which is at the upper limit of buildable residential pitch for a staircase. In practice that means it is strictly space-saving and best reserved for secondary access. Its Blondel value of 25.0 inches lands right in the 24–25 inch Blondel comfort band, so it should feel natural underfoot. Across a typical flight of about 14 treads, the 9-inch tread depth works out to roughly 9.8 feet of horizontal run — a compact footprint. Note that this pairing does not meet the residential IRC because the 8-inch riser exceeds the IRC's 7.75-inch maximum and the 9-inch tread is under the IRC's 10-inch minimum, so it would need adjustment before use in a typical home. ## When to choose it Reach for this pairing when floor space is tight and a steeper, more compact stair is acceptable — for example a secondary, basement, or loft stair rather than the primary staircase. Whatever your floor-to-floor height, the calculator below will hold the riser near 8 inches, divide the rise into uniform steps, and check the result against the code you select. ## Nearby combinations 7.25″ × 10.5″ , 6″ × 12″ , 7.75″ × 10″ , 7″ × 12″ ============================================================ FAQ ============================================================ URL: https://staircalculators.net/faq/ Home / FAQ Answers # Stair calculator FAQ 46 answers on stair geometry, winder and spiral specifics, building codes, and printing templates. Jump to: General stair geometry · Straight & deck stairs · Winder stairs · Spiral stairs · Code & compliance · Printing & templates ## General stair geometry ### How do I calculate the number of steps in a staircase? Divide the total floor-to-floor rise by your target riser height and round to the nearest whole number. Dividing total rise by that whole count gives the actual, uniform riser height. ### What is the difference between rise and run? Rise is the vertical height of a step or the whole stair; run is the horizontal depth. Total rise is floor-to-floor height; total run is the horizontal distance covered. ### Why is there one fewer tread than riser? The top riser lands on the floor above, which acts as the final tread, so 15 risers gives 14 treads. ### What is stringer length? The diagonal length of the board the steps are cut into, equal to the square root of total rise squared plus total run squared. ### What is a comfortable stair angle? Most comfortable domestic stairs fall between 30 and 38 degrees; codes cap the maximum steeper than that. ### What is the Blondel rule? A comfort formula: twice the riser plus the tread should total about 24 to 25 inches (550 to 700 mm), reflecting natural walking stride. ### What is the ideal riser and tread combination? A 7-inch riser with an 11-inch tread is the classic comfortable pairing, giving a Blondel value of 25. ### Do all steps have to be the same height? Yes. Codes require uniform risers and treads within a flight; the largest and smallest may differ by no more than 3/8 inch under the IRC. ### How do I measure total rise accurately? Measure the vertical distance from the finished lower floor to the finished upper floor, accounting for floor coverings. Measure at several points since floors are rarely perfectly level. ### What is the nosing on a stair? The nosing is the part of the tread that projects beyond the riser below it. The IRC requires a projection between 3/4 and 1 1/4 inches when treads are under 11 inches deep. ### Can stairs have open risers? Yes, but the opening must not allow a 4-inch sphere to pass through under the IRC, for child safety. ### What is a flush vs standard mount stair? A standard-mount stringer attaches below the deck or landing surface; a flush mount hangs the top tread level with the surface. The mount affects the top riser height calculation. ## Straight & deck stairs ### How many stringers does my deck stair need? At 16-inch on-center spacing, divide the width by 16 and add one. A 36-inch stair needs three to four stringers. ### Should I use a 2x10 or 2x12 stringer? A cut stringer must keep at least 3.5 inches of sound wood behind each notch. Most code-compliant residential steps require a 2x12; a 2x10 only works for shallow steps. ### When does a deck stair need a landing? Under the IRC a single flight may not exceed 147.0 inches of vertical rise without a landing. ### How deep should a stair landing be? At least as deep as the stair is wide, and never less than 36 inches in the direction of travel under the IRC. ### What is the maximum riser height for deck stairs? Under the IRC it is 7.75 inches; commercial stairs under the IBC are limited to 7.0 inches. ### What is stringer throat depth? The remaining width of sound wood behind a notch, measured perpendicular to the board edge. It must be at least 3.5 inches for a cut stringer to stay strong. ### How far apart should deck stair stringers be? Typically 16 inches on-center for 5/4 decking treads, or up to 24 inches for thicker 2x material, subject to span tables. ### Do exterior deck stairs follow the same code as interior? Largely yes for geometry, though deck-specific provisions (AWC DCA 6 stringer spans, footings, guards) also apply outdoors. ## Winder stairs ### What is a winder stair? A stair that turns using pie-shaped treads instead of a flat landing, narrow at the inside of the turn and wide at the outside. ### Why do winder stairs fail inspection? Most often the narrow end of a pie tread falls below minimum depth. Under the IRC the narrow end must be at least 6.0 inches and the walking-line depth at least 10.0 inches. ### Where is the winder walking line measured? At a fixed offset from the narrow side — 12.0 inches under the IRC. ### How do I make winder treads deeper at the narrow end? Increase the inner newel radius, reduce the turn angle per tread, or use fewer winder treads across the turn. ### How many winder treads make a 90-degree turn? Commonly three, each sweeping 30 degrees, though two or four are also used depending on space and tread-depth targets. ### Are winder stairs allowed by code? Yes, when each pie tread meets the narrow-end and walking-line minimums. They are common in loft and space-constrained layouts. ## Spiral stairs ### What is the minimum width for a spiral stair? Under the IRC the clear width at and below the handrail must be at least 26.0 inches. ### What is the maximum riser height for a spiral stair? Spiral stairs allow steeper risers than straight stairs — up to 9.5 inches under the IRC. ### How much headroom does a spiral stair need? The IRC requires at least 78.0 inches (6 feet 6 inches), measured from the leading edge of the tread. ### How do I size a spiral staircase? Choose the outer diameter to fit the opening, divide total rise by a target riser for the step count, and set rotation so each tread sweeps a usable arc at the walking line. ### What diameter spiral stair do I need? Common residential spirals range from 48 to 60 inches in diameter; larger diameters give deeper treads and easier use but consume more floor area. ### How many treads does a spiral stair have per turn? It depends on the rotation per tread. A full 360-degree turn typically uses 12 to 16 treads depending on the riser height and total rise. ## Code & compliance ### What is the maximum stair riser height? IRC residential: 7.75 inches; IBC commercial: 7.0 inches; UK Part K: 220 mm (8.66 inches). ### What is the minimum tread depth? IRC: 10.0 inches; IBC: 11.0 inches; Australian NCC: 240 mm (9.45 inches). ### What is the minimum headroom for stairs? The IRC requires 80.0 inches (6 feet 8 inches), measured vertically from the tread nosing line. ### How do US, UK and Australian stair codes differ? The US codes limit a flight by maximum vertical rise between landings; the UK and Australia limit by number of risers per flight (36 and 18). Riser and tread limits also differ. ### Does a calculator result guarantee code compliance? No. It flags likely compliance against published limits, but you must verify against the code edition your local authority enforces before building. ### What is the 3/8 inch rule? Within a flight, the largest and smallest riser, and the largest and smallest tread, may differ by no more than 3/8 inch under the IRC. It is among the most commonly failed requirements. ### What is the minimum stair width? The IRC requires 36 inches clear for residential stairs; the IBC commercial minimum is commonly 44 inches depending on occupancy. ### What changed between IRC 2018, 2021 and 2024? The stair geometry limits are unchanged across these editions. The 2024 IRC reorganized Chapter 3 and renumbered stairways from R311.7 to R318.7. ### Is Eurocode a single stair standard? No. Eurocode has no single prescriptive stair-dimension table; individual member states set stair geometry through national rules, so figures vary by country. ### What handrail height does code require? The IRC and IBC require handrails 34 to 38 inches above the nosing line. ## Printing & templates ### Can I print a full-scale stair template? The template prints the stringer notch layout at true 1:1 scale across tiled pages, so you can tape it to the lumber and mark cuts directly. Print at 100% / actual size, not 'fit to page'. ### How do I make sure my printer prints at the right scale? Each template includes a 1-inch calibration square. Print it, measure that square with a ruler, and confirm it is exactly one inch before cutting. ### What paper size do the templates use? Templates can be tiled for US Letter or A4. Choose the size that matches your printer before generating. ### Can I get a cut list instead of a full template? Yes. The spec-sheet output lists every dimension and the compliance status with clause references, suitable for the permit desk.