Stair calculator
Work out how many steps a staircase needs, the exact riser height, the total run and the stringer length.
Steps
- Treads
- Total run
- Stringer length
- Angle
How to use it
Measure the total rise: the vertical distance from the finished floor at the bottom to the finished floor at the top, in inches. Enter it with the tread depth you want. The calculator works out the number of risers, the exact height of each one, the number of treads, how far the stairs run horizontally, and how long the stringers must be.
How it's calculated
- Risers = total rise ÷ maximum riser height, rounded up.
- Riser height = total rise ÷ risers, so every step is exactly the same.
- Treads = risers − 1, because the top floor acts as the last step.
- Total run = treads × tread depth.
- Stringer length = √(rise² + run²).
| Total rise | Risers | Each riser | Treads at 10 in | Total run |
|---|---|---|---|---|
| 36 in (deck) | 5 | 7.2 in | 4 | 40 in |
| 96 in | 13 | 7.38 in | 12 | 120 in |
| 108 in | 14 | 7.71 in | 13 | 130 in |
Code limits
Most US homes follow the International Residential Code, which sets:
| Rule | Limit |
|---|---|
| Riser height | 7¾ in maximum |
| Tread depth | 10 in minimum |
| Variation within a flight | no more than ⅜ in between the tallest and shortest riser, or the deepest and shallowest tread |
| Headroom | 6 ft 8 in minimum |
Local codes can differ. Check with your building department before you cut stringers, especially for stairs inside a home.
Tips
- Measure to finished floors. If flooring hasn't gone in yet, add its thickness at the top and bottom, or the first and last steps won't match.
- The stringer length is a minimum. Buy lumber at least a foot longer to allow for cuts at the top and bottom.
- Uniform steps matter more than exact dimensions. People trip on a step that's even slightly different from the rest, which is why the code limits variation to ⅜ in.