IRC 2024 Stair Code 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

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.

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.