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
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.
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.
The top riser lands on the floor above, which acts as the final tread, so 15 risers gives 14 treads.
The diagonal length of the board the steps are cut into, equal to the square root of total rise squared plus total run squared.
Most comfortable domestic stairs fall between 30 and 38 degrees; codes cap the maximum steeper than that.
A comfort formula: twice the riser plus the tread should total about 24 to 25 inches (550 to 700 mm), reflecting natural walking stride.
A 7-inch riser with an 11-inch tread is the classic comfortable pairing, giving a Blondel value of 25.
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.
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.
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.
Yes, but the opening must not allow a 4-inch sphere to pass through under the IRC, for child safety.
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.
At 16-inch on-center spacing, divide the width by 16 and add one. A 36-inch stair needs three to four stringers.
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.
Under the IRC a single flight may not exceed 147.0 inches of vertical rise without a landing.
At least as deep as the stair is wide, and never less than 36 inches in the direction of travel under the IRC.
Under the IRC it is 7.75 inches; commercial stairs under the IBC are limited to 7.0 inches.
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.
Typically 16 inches on-center for 5/4 decking treads, or up to 24 inches for thicker 2x material, subject to span tables.
Largely yes for geometry, though deck-specific provisions (AWC DCA 6 stringer spans, footings, guards) also apply outdoors.
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.
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.
At a fixed offset from the narrow side — 12.0 inches under the IRC.
Increase the inner newel radius, reduce the turn angle per tread, or use fewer winder treads across the turn.
Commonly three, each sweeping 30 degrees, though two or four are also used depending on space and tread-depth targets.
Yes, when each pie tread meets the narrow-end and walking-line minimums. They are common in loft and space-constrained layouts.
Under the IRC the clear width at and below the handrail must be at least 26.0 inches.
Spiral stairs allow steeper risers than straight stairs — up to 9.5 inches under the IRC.
The IRC requires at least 78.0 inches (6 feet 6 inches), measured from the leading edge of the tread.
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.
Common residential spirals range from 48 to 60 inches in diameter; larger diameters give deeper treads and easier use but consume more floor area.
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.
IRC residential: 7.75 inches; IBC commercial: 7.0 inches; UK Part K: 220 mm (8.66 inches).
IRC: 10.0 inches; IBC: 11.0 inches; Australian NCC: 240 mm (9.45 inches).
The IRC requires 80.0 inches (6 feet 8 inches), measured vertically from the tread nosing line.
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.
No. It flags likely compliance against published limits, but you must verify against the code edition your local authority enforces before building.
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.
The IRC requires 36 inches clear for residential stairs; the IBC commercial minimum is commonly 44 inches depending on occupancy.
The stair geometry limits are unchanged across these editions. The 2024 IRC reorganized Chapter 3 and renumbered stairways from R311.7 to R318.7.
No. Eurocode has no single prescriptive stair-dimension table; individual member states set stair geometry through national rules, so figures vary by country.
The IRC and IBC require handrails 34 to 38 inches above the nosing line.
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'.
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.
Templates can be tiled for US Letter or A4. Choose the size that matches your printer before generating.
Yes. The spec-sheet output lists every dimension and the compliance status with clause references, suitable for the permit desk.