Stair Calculator
Calculate stair risers, treads, total run, and stringer length from total rise
Enter the floor-to-floor rise, a target riser height, and a tread depth. The calculator picks a whole number of risers, evens out the riser height, and gives the total run and the stringer length. For lumber volume, use the board foot calculator.
Calculator Inputs
Floor-to-floor height. 105 in is 8 ft 9 in.
Results
Enter values above to see your results
Layout math only. Local building code decides the legal riser, tread, headroom, and handrail.
How to use this calculator
- Measure the total rise in inches from finished floor to finished floor.
- Enter a target riser, often around 7 to 7.5 inches, and a tread depth, often 10 inches or more.
- Use the actual riser, the number of treads, the total run, and the stringer length.
How the calculation works
The number of risers is the total rise divided by the target riser, rounded to the nearest whole number. Actual riser height is the total rise divided by that count, so every riser matches. The number of treads is one less than the number of risers, because the top landing takes the place of the last tread.
Total run is treads × tread depth. Stringer length is the straight-line distance √(rise² + run²).
A common residential range
A common U.S. residential guideline keeps risers at about 7.75 inches or less and treads at about 10 inches or more. Local code, guards, and nosing rules control the built stair. This result is a layout, not a permit.
Worked example
105 inch rise, 7.5 inch target, 10 inch treads
105 ÷ 7.5= 14 risers at 7.5 in13 × 10= 130 in (10 ft 10 in)√(105² + 130²)= 167.11 in (13 ft 11.11 in)Tips & Best Practices
- •Measure to the finished floor surfaces, not the subfloor, if the finished floors are already chosen.
- •If the riser comes out above 7.75 inches, add a riser or lower the target.
Frequently Asked Questions
How many risers do I need?
Divide the total rise by the target riser and round to a whole number. Then divide the total rise by that count so each riser is the same height.
Why is there one fewer tread than risers?
Each riser is a vertical rise. The last rise lands on the upper floor, so that floor replaces the last tread.
How long is the stringer?
The stringer length here is the hypotenuse of the total rise and the total run. Cutting details, such as the thickness of the tread, are not included.
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