Stair Calculator

Enter the finished floor-to-floor rise and the app finds the riser count and exact riser height. Risers = round up(total rise ÷ target rise), then actual riser = total rise ÷ risers, which keeps every step identical as IRC R311.7.5.1 requires.

Get stringer length from the Pythagorean theorem: Stringer = √(Total Rise² + Total Run²). Cut stringers come from 2×12 stock, with notched stringers limited to roughly 7 ft spans and solid or housed stringers up to about 13 ft 3 in before an intermediate landing is required.

Flags every layout against IRC R311.7.5: maximum 7-3/4" riser, minimum 10" tread with a 3/4"–1-1/4" nosing (or 11" without nosing), and a maximum 3/8" difference between any two risers. Also reports the 2R+T sum so you stay in the comfortable 24"–25" band.

Check the 80" minimum headroom measured from the tread nosing to the plane above, and the 151" maximum vertical rise between landings. Warns when a long run needs an intermediate landing, and confirms the 36" minimum stair width and required handrail at four or more risers.

Build a full material list: 2×12 stringer boards cut to length, treads and risers sized from stair width and tread depth, stringer count at one per 16"–18" of width, and concrete volume for a landing or footing. A 36" stair typically uses three stringers.

Work in feet, inches, yards, meters, and centimeters. Output includes total run, stringer length, stair angle in degrees, riser and tread dimensions, lumber lengths, and concrete volume. All calculations, code checks, and cost estimates update automatically. Fully functional offline.