Stair calculator

Risers, treads, total run, stringer length and angle for a straight stair, checked against the 2021 IRC limits.

Code text last checked October 2, 2026. Check with your local building department. Found a mistake? Report an error.

How it's calculated

The calculator splits the total rise into equal risers no taller than your maximum, then works out the treads, total run, stringer length and angle.

risers = round up (total rise ÷ maximum riser)
riser height = total rise ÷ risers
treads = risers − 1 (the upper floor is the last step)
total run = treads × tread depth
stringer length = √(total rise² + total run²)
angle = arctan(total rise ÷ total run)

Worked example

A 108 in rise ÷ 7.75 in = 13.9, so 14 risers of 108 ÷ 14 = 7.714 in (about 7 11/16 in). That gives 13 treads; at 10 in each the total run is 130 in. The stringer is √(108² + 130²) = 169.0 in (about 14 ft 1 in) and the stair angle is 39.7°.

The stringer length here is the straight diagonal from the bottom to the top nosing line. Cut stringers need extra length for the bottom and top connections. Follow your framing plan.

Code limits used

1. Riser height not more than 7¾ in; the greatest riser in a flight may not exceed the smallest by more than ⅜ in: 2021 IRC R311.7.5.1.
2. Tread depth not less than 10 in, with the same ⅜ in tolerance: 2021 IRC R311.7.5.2.

Cities and states adopt and amend the IRC, and commercial buildings follow different rules. Confirm with your local building department before building.