This calculator checks a proposed stair’s riser height and tread depth against the dimensional limits in IBC 1011.5, the 2021 and 2024 International Building Code (commercial and dwelling-unit stairs), or IBC 1011.10 (spiral stairways). It is a reference estimate, not a code determination: confirm the adopted code edition and any local amendments with your local building department.
Before you use this: what this tool is and is not
This is a reference and estimating tool, not a code determination. It checks the numbers you enter against the dimensional limits stated in IBC 1011.5 and 1011.10. It does not apply any exception based on occupant load — no such stair-geometry relaxation is used here, because it was not confirmed against a primary source. Confirm the applicable edition and any local amendments with your Authority Having Jurisdiction (AHJ) before you rely on the result.
This page uses IBC Section 1011.5 (commercial stairs and the dwelling-unit exception) and IBC Section 1011.10 (spiral stairways), as they appear in the 2021 and 2024 International Building Code.
Check a proposed stair
Stair riser and tread calculator
Pick a stair type, enter your numbers, and this checks the individual riser and tread limits, plus the uniformity requirement where it applies.
The three rule sets this tool checks
Per IBC 1011.5, Stair Treads and Risers and IBC 1011.10, Spiral Stairways (both accessed 2026-09-17):
| Stair type | Riser height | Tread depth | Uniformity within one flight |
|---|---|---|---|
| Commercial / general (IBC 1011.5) | 4 in minimum, 7 in maximum | 11 in minimum | Largest and smallest riser, or largest and smallest tread, must not vary by more than 3/8 in |
| Dwelling unit (IBC 1011.5.2 Exception 3) | 7¾ in maximum (no minimum given here) | 10 in minimum | Not separately specified here — confirm with your AHJ |
| Spiral stairway (IBC 1011.10) | 9½ in maximum | 6¾ in minimum, measured 12 in from the narrow edge | Not specified for spiral stairs in the source used here |
Spiral stairways also need at least 78 in of headroom and 26 in of clear width, and are permitted only within a dwelling unit or from a space of 250 sq ft or less serving 5 occupants or fewer.
What this calculator deliberately leaves out
This tool checks only the three rule sets above. It does not apply any occupant-load-based exception to riser or tread dimensions, because no such exception was confirmed against a primary source during the research behind this page. If a design relies on a stair-geometry exception you have seen elsewhere, confirm the exact code section and its current text with your local building department before using it.
Where Groundbook fits
Groundbook’s document review already compares a dimensioned element across the sheets that describe it — for a stair, that means the riser and tread values shown on the plan, the section, and any enlarged detail — and flags where they disagree, the same cross-sheet consistency check described in the architectural drawing review checklist. It does not run the code-limit check on this page for you; use this calculator to check the numbers against IBC 1011.5 or 1011.10, then let Groundbook confirm the drawings themselves agree with each other.