Stair Rise and Run Calculator — IBC and IRC check

Riser height, tread depth, total run and stringer length from a total rise, checked against IBC 1011.5 and IRC R311.7 limits, which are not the same.

Stair Rise & Run Calculator

Enter the total floor-to-floor rise. Most calculators give you a riser height and stop — this one tells you whether that riser is legal, and under which code, because IBC and IRC do not agree.

Governing code

Units

Total rise, floor to floor (in)

Tread depth (in)

Target riser (in)

The same flight can pass one code and fail the other. The limits differ by 3/4″ of riser and 1″ of tread — enough to change the total run, and with it the floor opening.

——

Risers	—
Riser height	—
Treads	—
Total run	—
Stringer length	—
Angle from horizontal	—
2R + T (comfort rule)	—

Code values: IBC 1011.5 — riser 7" max, tread 11" min. IRC R311.7 — riser 7-3/4" max, tread 10" min. Riser uniformity within a flight is limited to 3/8" (IBC 1011.5.4 / IRC R311.7.5.1). Codes are amended by state and local jurisdiction — confirm the adopted edition with your building department. This is a design aid, not a compliance certification.