How this calculator works
The total rise is divided by the maximum allowed riser and rounded up to get the number of risers; dividing the rise by that number gives equal riser heights. There is one fewer tread than risers because the top floor acts as the last step.
Risers = round up( Total rise ÷ Max riser )
Riser height = Total rise ÷ Risers
Treads = Risers − 1
Total run = Treads × Tread depth
Stringer = √(Rise² + Run²)
Assumptions and tips
- IRC R311.7: riser ≤ 7¾ in, tread ≥ 10 in, headroom ≥ 6 ft 8 in, riser and tread variation within a flight ≤ 3/8 in.
- Stringer length is the sloped length; add for the top connection and bottom cut. Local codes can differ from the IRC.
Worked example
Using the default values in the calculator above:
| Input | Value |
|---|---|
| Total rise (floor to floor) | 108 in |
| Tread depth (run per step) | 10.5 in |
| Maximum riser height | 7.75 in |
| Result | Value |
|---|---|
| Risers | 14 risers |
| Riser height | 7.714 in |
| Treads | 13 treads |
| Total run | 136.5 in |
| Stringer length (approx.) | 14.5 ft |
| Stair angle | 38.4 ° |
Step by step:
- Risers = 108 ÷ 7.75 = 13.94 → 14
- Riser height = 108 ÷ 14 = 7.714 in
- Treads = 14 − 1 = 13; run = 13 × 10.5 = 136.5 in
- Stringer = √(108² + 136.5²) = 174.06 in
Stair layout by floor-to-floor height
7¾ in maximum riser and 10.5 in treads.
| Total rise | Risers | Riser height | Total run |
|---|---|---|---|
| 24 in | 4 risers | 6 in | 31.5 in |
| 36 in | 5 risers | 7.2 in | 42 in |
| 48 in | 7 risers | 6.857 in | 63 in |
| 96 in | 13 risers | 7.385 in | 126 in |
| 105 in | 14 risers | 7.5 in | 136.5 in |
| 108 in | 14 risers | 7.714 in | 136.5 in |
| 120 in | 16 risers | 7.5 in | 157.5 in |
Common mistakes to avoid
- Measuring rise to the subfloor instead of finished floor heights.
- Uneven top or bottom riser — the code allows only 3/8 in variation.
Frequently asked questions
How many steps for a 9 ft rise?
A 108 in rise with a 7¾ in maximum needs 14 risers of about 7.71 in, and 13 treads.
What is the 7-11 rule?
A rule of thumb for comfortable stairs: about a 7 in riser and an 11 in tread.