Stair Calculator
Calculate stair risers, riser height, tread depth, total run, and stringer length from your total rise. Meets standard building-code comfort ratios.
How this calculator works
Stairs must divide your total vertical rise into equal-height steps, each no taller than code allows. Enter your total rise, a maximum riser height, and your preferred tread depth, and the calculator finds the fewest equal risers that stay under your limit, then derives every other dimension from there.
Formula: Number of risers = ⌈total rise ÷ max riser⌉. Riser height = total rise ÷ number of risers. Total run = (risers − 1) × tread depth. Stringer length = √(rise² + run²).
Worked example
A 44-inch total rise, 7.75-inch maximum riser, 10-inch treads:
- Risers: ⌈44 ÷ 7.75⌉ = 6 steps
- Riser height: 44 ÷ 6 ≈ 7.33 in (comfortable, under the 7.75 cap)
- Treads: 6 − 1 = 5 treads
- Total run: 5 × 10 = 50 in
- Stringer length: √(44² + 50²) ÷ 12 ≈ 5.55 ft
- Comfort check: 2 × 7.33 + 10 ≈ 24.67 in (in the ideal 24–25 range)
Design reference
| Element | Code range | Comfortable target |
|---|---|---|
| Riser height | 4–7.75 in | 7–7.5 in |
| Tread depth | ≥ 10 in | 10–11 in |
| 2×riser + tread | — | 24–25 in |
How to measure
Measure total rise floor-to-floor with a level and tape, accounting for final flooring thickness top and bottom. If your run is limited by the space available, increase the riser height (up to code) to shorten the run, then re-check the comfort ratio.
Structural stair framing should follow local building code — verify riser, tread, and stringer sizing with your inspector before cutting.
Frequently asked questions
What is a comfortable riser height?
Building codes cap risers at 7.75 inches, and most people find 7 to 7.5 inches most comfortable. This calculator divides your total rise into equal risers no taller than your chosen maximum, so every step is the same height — uneven risers are the most common cause of stair trips.
What is the 2R + T rule?
Two times the riser height plus the tread depth should land between 24 and 25 inches for a comfortable stride. The calculator shows this value so you can adjust tread depth or riser count until it falls in range.
How do I measure total rise?
Measure vertically from the finished lower floor to the finished upper floor — not along the slope. Include any decking or flooring thickness that will be in place when the stairs are used.
How is stringer length calculated?
The stringer is the diagonal board that carries the treads, so its length is the hypotenuse of the total rise and total run: the square root of (rise squared + run squared). Buy stringer stock at least a foot longer than this to allow for the cuts at each end.
How many treads versus risers are there?
There is always one fewer tread than risers, because the top riser lands on the upper floor itself rather than a separate tread board.
Estimates only. Verify quantities with your supplier before purchasing.