Stairs are one of the most inspected parts of any job, and one of the most dangerous if they're wrong. Small inconsistencies trip people. These are the core rules for one- and two-family dwellings under the International Residential Code. Always confirm with your local building department, since states and cities amend the IRC.
The key dimensions
| Item | Rule |
|---|---|
| Riser height | 7¾" maximum |
| Tread depth | 10" minimum (nose to nose) |
| Variation | ⅜" max between largest and smallest riser or tread |
| Width | 36" minimum |
| Headroom | 6′8″ minimum |
| Handrail height | 34–38" |
| Guard openings | 4" sphere must not pass |
Laying out a flight
- Measure the total rise from finished floor to finished floor.
- Divide by the maximum riser and round up to get the number of risers.
- Divide the total rise by that number for the exact riser height.
- Treads = risers − 1. Total run = treads × tread depth.
- Check headroom along the whole flight against the floor above.
A comfortable stair often uses risers around 7–7½" with 10½–11" treads.
Common failures
- The top or bottom riser is a different height because the floor finish wasn't allowed for.
- Headroom too low under a beam or the stair opening.
- Balusters spaced just over the 4" limit.
- Missing handrail where one is required.
The stair calculator runs these checks as you type.
This guide is general information for estimating. It is not engineering, legal or tax advice. Check local codes and your inspector for your project.