Stair Calculator
Calculate riser height, number of steps, total run, angle and stringer length – and check them against the building code.
How it works
Enter the total rise from finished floor to finished floor, the tallest riser you allow and the tread depth. The calculator divides the rise into equal risers no taller than your maximum. There is always one tread fewer than risers, because the top step is the upper floor.
Example: a 108 in total rise with a 7¾ in maximum gives 14 risers of 7.71 in. With 10 in treads the stair is 130 in long, rises at 37.6° and needs a stringer about 169 in long.
US code limits for homes
- Riser height: 7¾ in maximum (IRC R311.7.5.1)
- Tread depth: 10 in minimum
- Headroom: 6 ft 8 in
- Risers and treads within a flight may differ by no more than ⅜ in
Commercial and public buildings follow the IBC: risers 4–7 in and treads at least 11 in. Local codes can be stricter.
A comfortable stair
A rule from the 17th century still works: 2 × riser + tread should be about 24–25 in (61–64 cm), the length of a normal stride. The example above is 25.4 in – at the steep end, as a minimum-tread home stair usually is.
Frequently asked questions
How many steps do I need for 9 feet?
A 108 in rise with risers of at most 7¾ in needs 14 risers and 13 treads.
What is the best stair angle?
Between about 30° and 37° for stairs inside homes.