Stair Rise and Run Calculator
Lay out a staircase from a total rise: number of steps, exact riser height, total run and stringer length, with a comfort check.
How it works
risers = round(total rise ÷ target riser) · actual riser = total rise ÷ risers · treads = risers − 1 · total run = treads × run · stringer = √(rise² + run²)
You cannot have a fractional step, so the rise is divided by a comfortable target height and rounded to a whole number of risers; dividing the total rise back by that count gives the exact, equal riser height. There is always one fewer tread than riser, because the top riser lands on the floor above. The stringer follows the hypotenuse of the rise and run, and the "2 × riser + run" figure — ideally 24 to 25 in — is the classic check for a comfortable, safe pitch.
Worked example
A 108 in floor-to-floor rise with a 7.5 in target: 108 ÷ 7.5 = 14.4, rounded to 14 risers of exactly 7.714 in. With 13 treads at 10 in the total run is 130 in, the stringer is √(108² + 130²) ≈ 169 in, and 2 × 7.714 + 10 = 25.4 in — just past the 24–25 in comfort band, so trimming the run to 9 in would bring it in.
Frequently asked questions
What is a comfortable stair riser height?
Most codes cap risers around 7.75 in and treads at a minimum of 10 in of run. Comfortable stairs keep every riser equal and land the "2 × riser + run" total near 24 to 25 in.
Why is there one fewer tread than riser?
The top riser brings you level with the upper floor, and the floor itself acts as the last tread. So a flight with 14 risers has 13 treads between floors.
How long a stringer board do I need?
The stringer spans the diagonal of the total rise and run, so it is the square root of rise squared plus run squared. Add length for the top and bottom connections and buy the next standard size up.
Related calculators
Estimates only — add for waste and confirm against local building codes and supplier specs.