Stair Calculator
Turn your floor-to-floor rise into a buildable staircase — number of steps, riser height, total run and stringer length, with code checks.
Updated October 2026
Based on typical US residential code (IRC): max riser 7.75", min tread 10", and the comfort rule 2×riser + tread ≈ 24–25". Always confirm your local building code and headroom before cutting stringers.
This stair calculator turns a single measurement — the total floor-to-floor rise — into a buildable staircase: how many steps, the exact riser height, the total horizontal run and the stringer length to cut. Enter your rise and a target step height, and it divides the rise into equal risers and works out the rest.
It also checks the numbers against typical US residential code: risers no taller than 7.75 inches, treads at least 10 inches deep, and the old carpenter's comfort rule that twice the riser plus the tread should land between 24 and 25 inches. Even risers matter — an uneven last step is both a code fail and a trip hazard.
How to use it
- 1Measure the total rise from the lower finished floor to the upper finished floor.
- 2Enter that rise and a target riser height (7–7.75 inches is typical).
- 3Set your tread depth (10–11 inches is common).
- 4Read the step count, actual riser height, total run and stringer length, with code checks.
Frequently asked questions
How do I calculate the number of stairs?+
Divide the total floor-to-floor rise by your target riser height and round to a whole number — that's the number of risers (steps). Then the actual riser height is the total rise divided by that count, which keeps every step equal.
What's the maximum riser height and minimum tread?+
Under the US residential code (IRC), risers can be at most 7.75 inches and treads at least 10 inches deep. Many builders also follow the comfort rule that 2 × riser + tread should equal about 24–25 inches for a stair that feels natural to climb.
What is the stringer length?+
The stringer is the diagonal board that supports the steps. Its length is the hypotenuse of the total rise and total run — √(rise² + run²) — so you know the minimum board length before accounting for cuts and overhang.
Why must all risers be equal?+
Code requires the difference between the tallest and shortest riser in a flight to be very small (about 3/8 inch). Uneven steps — especially a short or tall final step — are a common trip hazard and will fail inspection, which is why the calculator spreads the rise evenly.
Related calculators
Estimate how many gallons of paint you need for a room based on wall area.
Calculate area in square feet for rooms and projects, plus total material cost.
Work out what any appliance costs to run — per day, month and year — from its wattage and your electricity rate.
Estimate how many solar panels you need, the system size and cost, and the payback period — worked back from your power bill, with the 30% tax credit.