Stair Geometry: Rise, Run, and Local-Code Review Guide
Calculate preliminary stair rise, run, and stringer geometry, then compare the result with the locally adopted code and project requirements.
Start with finished-floor geometry
Total rise is the vertical distance between the finished floor levels served by the stair. Divide that measured rise by a target riser height to explore a preliminary number of risers, then recalculate the exact riser height from the whole-number result. The calculator is useful for this geometry check, but it does not determine which code applies to the project.
The 2024 IBC page for stair risers and treads includes different provisions and exceptions by occupancy. For example, it lists general and specified residential dimensions separately. Always use the code adopted by the authority having jurisdiction and the project’s occupancy classification—not a generic online value—as the compliance reference.
Calculate run as geometry, then review the adopted code
Total run is the number of treads multiplied by the chosen unit run. The IBC section cited below distinguishes general rectangular-tread dimensions from certain residential and other exceptions. That is why the calculator should be used to compare options, while the final tread depth, nosing, landings, guards, handrails, and accessibility requirements are reviewed against the applicable local rules.
Check the items the calculator does not decide
The Pythagorean theorem can estimate a sloped stringer length from rise and run, but a buildable stair also depends on headroom, landings, framing, opening geometry, guards, handrails, nosings, material details, and the adopted code. Measure the actual site and have the responsible contractor, designer, or code official review the final layout where required.
- Measure the finished floor-to-floor rise, not only rough framing dimensions.
- Use the same units throughout the preliminary rise-and-run calculation.
- Check the locally adopted code, occupancy, and any amendment before cutting stringers or ordering parts.
- Treat the calculated stringer length as a geometry check; verify framing, connections, and safety details separately.
Sources and further reading
- 2024 IBC Section 1011.5.2 — Riser height and tread depth — International Code Council; Published IBC dimensions and listed exceptions; the locally adopted code controls.