How it works
The formula
risers = total rise ÷ 7.75 in, rounded up · riser height = total rise ÷ risers
treads = risers − 1 · total run = treads × tread depth
stringer = √(total rise² + total run²)
treads = risers − 1 · total run = treads × tread depth
stringer = √(total rise² + total run²)
The code limits we check
- From the 2021 International Residential Code, R311.7 (as adopted): risers no more than 7 3/4 in, treads at least 10 in, and no more than 3/8 in difference between the biggest and smallest of either in a flight.
- A flight rises no more than 12 ft 7 in (151 in) between floors or landings; at least 36 in wide; 6 ft 8 in of headroom.
- A nosing of 3/4 to 1 1/4 in on each tread, unless treads are at least 11 in deep. A handrail 34 to 38 in high on at least one side once there are four or more risers.
- Comfort: designers aim for 2 risers + 1 tread between 24 and 25 in, a rule of thumb from Architectural Graphic Standards (as cited by Autodesk), not a code requirement.
- Your town may amend the code (California, for one, asks for taller guards). Check with your building department before you cut.
Steps by total rise
| Total rise | Risers | Riser height | Run (10 1/2 in treads) |
|---|---|---|---|
| 24 in | 4 | 6 in | 2.6 ft |
| 36 in | 5 | 7 3/16 in | 3.5 ft |
| 48 in | 7 | 6 7/8 in | 5.3 ft |
| 72 in | 10 | 7 3/16 in | 7.9 ft |
| 96 in | 13 | 7 3/8 in | 10.5 ft |
| 108 in | 14 | 7 11/16 in | 11.4 ft |
| 120 in | 16 | 7 1/2 in | 13.1 ft |
| 144 in | 19 | 7 9/16 in | 15.8 ft |
Questions people ask
How many steps do I need?
Divide the total rise by 7 3/4 in and round up: that's the number of risers. A 9 ft (108 in) rise takes 14 risers of 7 11/16 in, with one fewer tread than risers.
What is the maximum step height?
7 3/4 in under the International Residential Code, with treads at least 10 in deep. Commercial buildings follow a stricter code (7 in risers, 11 in treads).
How long should a stair stringer be?
The diagonal of the total rise and total run, plus a little for the top and bottom cuts. Stringers are usually cut from 2×12s, which come in 2 ft steps.