Stair Calculator
Calculate stair rise, run, and stringer length from your total height. Get the number of steps and code-friendly riser and tread dimensions.
Floor-to-floor vertical height
Ideal: 7–7.75 in (code max 7.75 in)
Min recommended: 10–11 in
Number of Steps (Risers)
15
Actual Riser Height
7.27 in
Within comfortable range (6.5–7.75 in)
Number of Treads
14
Always one fewer than risers
Total Run (horizontal length)
140.00 in
11.67 ft
Stringer Length
177.43 in
14.79 ft · diagonal hypotenuse
Code Guidance Notes
- ▸Actual riser: 7.27 in — comfortable/standard range is 7–7.75 in; most codes cap at 7.75 in.
- ▸Tread depth: 10.00 in — minimum recommended is 10–11 in.
- ▸Riser + tread = 17.27 in (rule of thumb: 17–18 in).
- ▸2×riser + tread = 24.53 in (rule of thumb: 24–25 in).
Frequently Asked Questions
What is a comfortable stair rise and run?
A comfortable riser height is between 7 and 7.75 inches — most building codes cap riser height at 7.75 in. Tread depth (run) should be at least 10–11 inches. A handy rule of thumb: riser + tread ≈ 17–18 inches, or 2×riser + tread ≈ 24–25 inches. Staying within these ranges produces stairs that feel natural to climb without fatigue.
How many steps do I need for my staircase?
Divide the total rise (floor-to-floor height in inches) by your target riser height, then round to the nearest whole number. That gives you the number of risers (steps). The number of treads is always one fewer than the number of risers, because the upper floor serves as the final landing. For example, a 109-inch rise with a 7.5-inch target riser yields 15 risers and 14 treads.
How do I calculate stair stringer length?
The stringer is the diagonal structural board that supports the steps. Its length is the hypotenuse of the right triangle formed by the total rise (vertical) and total run (horizontal). Use the Pythagorean theorem: stringer length = √(totalRise² + totalRun²). For a stair with a 109-inch rise and 140-inch total run, the stringer is approximately 177.4 inches (≈ 14.8 feet).