Stair Calculator
Enter the total height the stairs must climb, the riser height you are aiming for and the tread depth. The calculator works out the number of steps and the exact size of each.
Type a number and the answer appears straight away.
Number of steps (risers)15Each riser 7.2 in high
- Treads
- 14
- Total run
- 147 in (12.25 ft)
- Stringer length
- 182.4 in (15.2 ft)
- Stair angle
- 36.3 degrees
- Comfort check (2 risers + 1 tread)
- 24.9 in, ideal
Comfortable stairs keep two risers plus one tread between 24 and 25 inches. Building codes vary, so confirm the limits with your local authority before you build.
The math behind it: Stairs
risers = total rise / target riser height, rounded; actual riser = total rise / risers; total run = (risers - 1) x tread depth
A total rise of 108 inches (9 feet) with a target riser of 7.25 inches gives 15 risers of 7.2 inches each. With 10.5 inch treads there are 14 treads, a total run of 147 inches and a stringer about 182.4 inches long.
Comfortable stairs keep two risers plus one tread between 24 and 25 inches. Building codes set their own limits, so confirm them locally before you build.
Common questions
How do I calculate stairs?
Divide the total rise by the riser height you want and round to a whole number of steps. Then divide the total rise by that number to get the exact riser height.
What is the standard stair rise and run?
Many US building codes allow a riser of up to 7.75 inches and require a tread at least 10 inches deep. Around 7 to 7.5 inches of rise with a 10 to 11 inch tread is comfortable.
How many steps do I need for 9 feet?
15 steps with risers of 7.2 inches each. Nine feet is 108 inches, and 108 / 15 = 7.2.
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