Stair Rise & Run Rules of Thumb
IRC 2021 code requirements for residential stairs. Stairs are structural — errors here are safety issues, not cosmetic ones. Always verify with your local adopted code version.
IRC code requirements
| Rule | Requirement |
|---|---|
| Max riser height | 7¾″ (7.75″) |
| Min riser height | 4″ |
| Min tread depth | 10″ |
| Nosing projection | ¾″ to 1¼″ |
| Stair width (clear) | 36″ minimum |
| Headroom clearance | 6′-8″ minimum |
| Handrail required when | 4 or more risers |
| Riser consistency | 3/8″ max variation |
Common code-compliant combinations
The “18-inch rule”: rise + run should total ~17–18 inches for a comfortable stair. Total run = (steps − 1) × tread depth.
| Riser | Tread | Sum | Run (9 steps) | Run (12 steps) |
|---|---|---|---|---|
| 7.0″ | 11.0″ | 18.0″ | 5′-3″ | 7′-0″ |
| 7.25″ | 10.75″ | 18.0″ | 5′-5¼″ | 7′-3″ |
| 7.5″ | 10.5″ | 18.0″ | 5′-7½″ | 7′-6″ |
| 7.75″ | 10.25″ | 18.0″ | 5′-9¾″ | 7′-9″ |