Stair Calculator
Plan a straight stair by estimating risers, treads, total run, stringer length, and slope angle.
Stair inputs
Number of risers:
Actual riser height: in
Number of treads:
Total run: in
Stringer length: in
Stair angle: deg
Why the riser count is rounded
The total rise (floor-to-floor height) must be divided into a whole number of equal risers, so the calculator rounds your target riser height to the nearest value that divides evenly into the total rise — every step in a staircase needs to be the same height, since uneven risers are a well-known trip hazard. The stringer length (the diagonal board supporting the steps) is then found using the Pythagorean theorem on the total rise and total run.
Frequently asked questions
Why does the actual riser height differ slightly from my target? Since the total rise must split evenly across a whole number of steps, the calculator adjusts to the closest riser height that divides the total rise exactly — a small deviation from your target is normal and keeps every step equal.
What riser and tread dimensions are typically used? Many residential building codes call for risers around 7–7.75 inches and treads around 10–11 inches, though exact requirements vary by jurisdiction — always check your local building code before construction.
Why does the number of treads equal risers minus one? The top riser leads onto the upper floor itself (which serves as the final "tread"), so a staircase with, say, 14 risers only needs 13 physical tread boards below the top landing.