How it works
A stair with equal risers has one more riser than treads, because the top surface of the floor above acts as the last tread. Divide the total rise by your preferred riser height and round to the nearest whole number of risers, then divide the rise by that number for the exact riser height.
The total run is the number of treads times the tread depth. The stringer’s long edge is the hypotenuse of the rise and run. The first riser is cut short by the thickness of the tread material so that every finished riser measures the same.
Worked example
A 56 in rise with a 7-1/2 in preferred riser, 10 in treads, 1 in tread material, and a 2×12 stringer:
- Risers = round(56 in ÷ 7.5 in) = 7
- Riser height = 56 ÷ 7 = 8 in
- Total run = 6 treads × 10 in = 60 in
- Stringer length = √(56² + 60²) ÷ 12 = 6.84 ft
- Angle = arctan(8 ÷ 10) = 38.7°
- Bottom riser cut = 8 − 1 = 7 in
| Input | Value |
|---|---|
| Total rise | 56 in |
| Preferred riser height | 7.5 in |
| Tread depth (run per step) | 10 in |
| Tread thickness | 1 in |
| Stringer board depth | 11.25 in |
| Result | Value |
|---|---|
| Number of risers | 7 risers |
| Riser height | 8 in |
| Treads (steps to cut) | 6 treads |
| Total run | 60 in |
| Stringer length (long edge) | 6.84 ft |
| Stair angle | 38.7 ° |
| Uncut depth left at the notch | 5 in |
| Bottom riser cut (subtract tread thickness) | 7 in |
Assumptions and limits
- Limits shown come from the International Residential Code (R311.7.5): risers no more than 7-3/4 in, treads at least 10 in, and no more than 3/8 in variation between risers or treads in a flight. Your local code may differ.
- Landing sizes, handrails, guards, headroom, and stair width are not calculated here.
- Stringer strength and span depend on lumber grade and species; this tool checks geometry only.
Common questions
How many steps do I need for a given rise?
Divide the total rise by a comfortable riser height, often around 7 to 7-1/2 in, and round. The calculator then splits the rise equally so every riser matches.
What are the code limits on rise and run?
The IRC allows a maximum riser of 7-3/4 in and a minimum tread of 10 in for residential stairs, with no more than 3/8 in variation within a flight. Check your local amendments.
Why is the bottom step cut shorter?
The treads add their thickness at the bottom step, so the first riser is cut short by that amount to keep every finished riser equal.
How much wood should be left at the notch?
Enough to carry the load; the amount depends on grade, span, and species. The calculator reports the remaining depth so you can check it against a span table or your engineer.
Sources
- International Residential Code R311.7.5.1 (risers) and R311.7.5.2 (treads).
- Stair geometry from right-triangle trigonometry; the notch depth is the perpendicular distance from the inside corner to the nosing line.
- Read them: ICC: 2021 IRC R311.7.5.1 Risers
Updated 2026-09-30