Treads must be at least 10 inches deep under the IRC (11 inches commercial). The consistency rule matters as much as the maximum — a single odd step is what actually trips people, which is why stair layouts divide the total rise into perfectly equal risers.
Comfortable stairs usually land below the legal maximum: 7 to 7.5 inch risers with 10.5 to 11 inch treads. The old carpenter's check — two risers plus one tread between 24 and 25 inches — still works.
Stair code limits (US)
| Rule | Residential (IRC) | Commercial (IBC) |
|---|---|---|
| Max riser | 7¾ in (196 mm) | 7 in (178 mm) |
| Min tread | 10 in (254 mm) | 11 in (279 mm) |
| Max variation | ⅜ in (10 mm) | ⅜ in (10 mm) |