How to use it
- Measure total rise from finished floor to finished floor.
- Set the maximum riser height and tread depth allowed by your code.
- Enter the stair width for the stringer count.
The formula
Risers = total rise ÷ max riser (rounded up)
Treads = risers − 1
Stringer ≈ √(rise² + run²)
Worked example
| Total rise (floor to floor) | 108 in |
| Maximum riser height | 7.75 in |
| Tread depth (run) | 10 in |
| Stair width | 36 in |
Result
| Number of risers | 14 |
| Riser height | 7.71 in |
| Number of treads | 13 |
| Total run | 130 in |
| Stringer length (approx.) | 14.08 ft |
| Stair angle | 39.7 ° |
| Stringers (16 in o.c.) | 3 |
| Comfort check 2R + T (ideal 24–25 in) | 25.4 in |
Tips before you order
- The IRC limits risers to 7¾ in and requires treads of at least 10 in.
- Riser heights within a flight may not vary by more than ⅜ in.
Questions
How many steps for a 9 ft rise?
108 in ÷ 7.75 in rounds up to 14 risers of about 7.7 in, with 13 treads.