Stair Rise and Run: Code Rules and How to Calculate
Short answer: under the International Residential Code (IRC), each stair riser can be no more than 7¾ inches tall and each tread at least 10 inches deep. In a flight, the tallest riser and deepest tread can’t exceed the smallest by more than ⅜ inch. Many builders aim for about 7 to 7½ in risers and 10½ to 11 in treads.
To lay out your stairs from the floor-to-floor height, use the stair calculator. It finds the number of steps, the exact riser height, the total run and the stringer length.
Residential stair rules (IRC R311.7)
| Rule | Requirement |
|---|---|
| Riser height | 7¾ in maximum |
| Tread depth | 10 in minimum |
| Variation within a flight | ⅜ in maximum |
| Headroom | 6 ft 8 in minimum |
| Handrail | Required with 4 or more risers |
As quoted in Kitsap County’s residential inspection checklist. Your local code may differ, so check before you build.
How to work out rise and run
- Measure the total rise: finished floor to finished floor. Say 108 inches.
- Number of risers: divide by your target riser and round up: 108 ÷ 7.5 = 14.4, so 15 risers.
- Exact riser height: 108 ÷ 15 = 7.2 in.
- Treads: one fewer than risers (the top floor is the last step): 14 treads.
- Total run: 14 × 10.5 in = 147 in, or 12¼ ft of floor space.
Steps for common heights
| Total rise | Risers | Riser height | Total run (10.5 in treads) |
|---|---|---|---|
| 24 in | 4 | 6.00 in | 31.5 in |
| 36 in | 5 | 7.20 in | 42 in |
| 96 in | 13 | 7.38 in | 126 in |
| 108 in | 15 | 7.20 in | 147 in |
| 120 in | 16 | 7.50 in | 157.5 in |
Common questions
What is the maximum riser height for stairs?
7¾ inches under the IRC (R311.7.5.1).
What is the minimum tread depth?
10 inches under the IRC (R311.7.5.2), measured without the nosing.
How many steps do I need for 9 ft?
For 108 inches with a 7.5 in target: 15 risers of 7.2 in and 14 treads.