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Stair Calculator
Split a floor-to-floor height into equal steps: number of risers, riser height, tread depth, angle, and total run, checked against the 2R + T comfort rule and US code limits.
Stair Calculator: The total rise is divided into the number of risers nearest 17.5 cm each. With no run given, the tread is set so that twice the riser plus the tread is 63 cm, Blondel's rule for a comfortable stride; with a run, it is the run divided by the number of treads, one fewer than risers because the upper floor is the last step. The result is checked against the International Residential Code's limits of a 7¾ in riser and a 10 in tread. Runs 100% locally in your browser with zero server file uploads.
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Without a total run, the tread is chosen so that 2 × riser + tread is 63 cm, Blondel's rule for a comfortable stride. The US limits shown are those of the International Residential Code; local rules differ, so check yours before building. Tread depth here is the going, measured nosing to nosing, without the overhang.
A worked example
A floor-to-floor height of 280 cm divides into 16 risers of 17.5 cm. Blondel's rule gives a tread of 63 − 2 × 17.5 = 28 cm, so 15 treads take 4.2 m of floor, at an angle of 32°.
For lumber quantities, see the board foot calculator.
Measuring the rise
Measure from the finished lower floor to the finished upper floor, including floor coverings on both. A difference of even a centimetre between the first or last step and the others is a tripping hazard, which is why every riser should be equal.
How to use it
- Choose millimetres, centimetres, or inches and enter the total rise from floor to floor.
- Optionally enter the run available, or a number of risers; −1 and +1 change the count.
- Read the riser height, tread depth, and angle, and whether they fall within the limits shown.
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Frequently asked questions
Why is there one tread fewer than risers?
The last riser takes you onto the upper floor itself, which acts as the final tread.
What is a comfortable stair?
Most guides aim for 2 × riser + tread between about 60 and 65 cm (24 to 25½ in), and an angle of roughly 30 to 35°.
Do these limits apply where I live?
Not necessarily: the US limits are from the International Residential Code, and other countries and towns set their own. Check the local rules before building.
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