Building a staircase requires every riser to be exactly the same height — uneven risers are one of the most common trip hazards in residential construction. Our stair calculator starts from your total rise and a target riser height, then works out the exact numbers needed for a safe, code-compliant build.
How the math works
Number of risers = round(total rise ÷ target riser height)
Actual riser height = total rise ÷ number of risers
Number of treads = number of risers − 1
Total run = number of treads × tread depthRounding to a whole number of risers, then recalculating the actual height, guarantees every single riser in the finished staircase is identical — you can’t build “15.43 risers,” so the target height is always an approximation that gets corrected once the whole-number count is fixed.
Example
108 inches of total rise (9 feet floor-to-floor), targeting 7-inch risers, 10-inch tread depth:
- Risers: round(108 ÷ 7) = round(15.43) = 15
- Actual riser height: 108 ÷ 15 = 7.20 in
- Treads: 15 − 1 = 14
- Total run: 14 × 10 = 140 in
Why treads = risers − 1
Each riser is a vertical step up; treads are the horizontal surfaces between them. The upper floor itself counts as the final “step,” so a 15-riser staircase only needs 14 physical tread boards.
Check your local code
Most residential codes cap riser height around 7–7.75 inches and require a minimum tread depth (commonly 10 inches) — requirements vary by jurisdiction and stair type, so verify against your local building code before finalizing a design.