Stair Calculator

Design code-compliant stairs with correct riser height, tread depth, and stringer length per IRC Section R311. Outputs cut dimensions.

Stair layout is one of the most code-sensitive calculations in residential framing. The IRC specifies maximum riser height (7¾"), minimum tread depth (10"), and maximum dimensional variation between risers (⅜"). This calculator takes total rise (floor-to-floor height) and produces the number of risers, individual riser height, tread depth, and stringer length — all checked against IRC Section R311 limits.

Frequently Asked Questions

What are the IRC limits for stair risers?

IRC R311.7.5.1 limits maximum riser height to 7¾" (196 mm). The maximum variation between any two risers is ⅜".

What is the minimum tread depth per code?

IRC R311.7.5.2 requires a minimum tread depth of 10" (254 mm). Nosing, if provided, must project between ¾" and 1¼" beyond the riser face.

How do I calculate stringer length?

Stringer length is the hypotenuse of a right triangle formed by the total rise and total run. This calculator uses the Pythagorean theorem: √(total_rise² + total_run²).

Estimates are for planning purposes only. Verify quantities with your supplier and confirm code requirements with your local building department.