Stair Stringer Calculator
Enter the total rise to get the number of steps, the riser height, the total run, and the stringer length and angle, checked against common IRC limits.
- Riser height
- Treads
- Total run
- Stair angle
- Throat left
- Stringers
- Comfort check
- Stringer Length
Stair List
Stairs you add are saved in this browser.
| Stair | Rise | Risers | Riser | Run | Stringer | Boards | Remove |
|---|
How to Lay Out a Stair Stringer
Divide the total rise by the tallest riser you'll allow and round up to get the number of risers. Then divide the rise by that number so every step is the same height. There's one less tread than risers, because the top step is the floor or deck itself.
The ⌈ ⌉ brackets mean round up. The stringer length is the diagonal along the nosings; buy a board at least a foot longer to allow for the top and bottom cuts.
Worked Example
Common IRC Stair Limits
| Item | Limit (2021 IRC, R311.7) |
|---|---|
| Riser height | 7¾″ maximum |
| Tread depth | 10″ minimum, nosing to nosing |
| Variation | Largest riser or tread no more than ⅜″ bigger than the smallest in a flight |
| Nosing | ¾″ to 1¼″ where treads are less than 11″ deep |
| Width | 36″ minimum |
| Headroom | 6′ 8″ minimum |
| Handrail | Required with four or more risers, 34″ to 38″ above the nosings |
Your local code may differ. Commercial stairs follow the IBC, with a 7″ maximum riser and 11″ minimum tread.
Tips for Cutting Stringers
Lay out the steps with a framing square and stair gauges set to the riser and tread. Cut the bottom of the stringer shorter by the thickness of one tread, so the first step comes out the same height as the rest once treads are on. Don't overcut the corners; finish them with a handsaw. A common rule of thumb is to keep at least 3½″ of solid wood (the throat) below the notches, and more for long spans.