🪜 Stair Calculator (Rise & Run)
Enter the total floor-to-floor rise, a target riser height and the tread depth to get the number of risers, the actual riser height, the run and the stringer length.
15
risers
7.467 in
actual riser
140 in
total run (14 treads)
179.3 in
stringer length
The number of risers is the total rise divided by your target riser height, rounded to a whole number; the actual riser is the rise divided by that count. There\'s one fewer tread than risers, so the run is treads × tread depth, and the stringer length is √(rise² + run²). US IRC limits: riser ≤ 7¾″, tread ≥ 10″ — always confirm your local building code. 🔒 In your browser.
How the stair calculator (rise & run) works
The number of risers is the total rise divided by your target riser height, rounded to a whole number; the actual riser height is the total rise divided by that count (so every step is equal). A flight always has one fewer tread than risers, so the total run is treads × tread depth, and the diagonal stringer length is √(rise² + run²) by Pythagoras. The tool flags if the riser or tread falls outside common code limits.
US IRC limits are a maximum 7¾-inch riser and a minimum 10-inch tread, and all steps in a flight must be within about ⅜ inch of each other — which is why you divide into equal risers rather than leaving an odd last step. Codes vary by country and by residential vs commercial, so always confirm locally; comfort rules of thumb include "riser + tread ≈ 17–18 in" and "2×riser + tread ≈ 25 in".
Frequently asked questions
How do you calculate the number of stairs?
Divide the total floor-to-floor rise by a comfortable riser height (around 7–7.75 in) and round to a whole number. That's the number of risers; the actual riser height is the total rise divided by it, so every step is equal.
How do you calculate stringer length?
It's the diagonal of the staircase: √(total rise² + total run²). If the rise is 112 in and the run 140 in, the stringer is about 179 in. Add length for how it meets the floor and landing.
What is the maximum riser height?
Under the US IRC, 7¾ inches for residential stairs; the minimum tread depth is 10 inches. Commercial codes are stricter. Steps must also be uniform — no more than about ⅜ inch difference between them.
What is a comfortable stair angle?
Most comfortable stairs land between about 30° and 37°. A common comfort rule is riser + tread ≈ 17–18 inches, or 2 × riser + tread ≈ 25 inches. Steeper stairs save space but are harder to climb.
Why is there one fewer tread than risers?
Because the top "tread" is the landing or upper floor itself, so it isn't counted. A flight with 15 risers has 14 treads. The tool accounts for this when computing the run.