How we worked it out
Updated as you change the numbers.
- Risers = total rise ÷ maximum riser = 108 ÷ 7.75 = 13.94, rounded up to 14.
- Riser height = 108 ÷ 14 = 7.714 in.
- Treads = risers − 1 = 13. Total run = 13 × 10 in = 130 in.
- Stringer = √(rise² + run²) = √(108² + 130²) = 169 in.
Method and assumptions
All risers in a flight must be the same height (the IRC allows only 3/8 in of difference), so the total rise is divided into the fewest equal steps that stay under your maximum. There is one fewer tread than risers, because the upper floor serves as the last step.
The stringer length is the diagonal of the rise and run (Pythagoras). Buy stringer stock longer than this to allow for the cuts at the top and bottom.
Tips
- Measure the rise to the finished floor surfaces, accounting for flooring you have not laid yet.
- Stairs with four or more risers need a handrail under the IRC, and guards where the open side is more than 30 in above the floor.
- Local codes can differ from the IRC. Check with your building department before you cut stringers.
Questions
How many steps do I need for a 9 ft rise?
A 9 ft (108 in) rise needs 14 risers of about 7.71 in each, with the IRC limit of 7 3/4 in. With 10 in treads, the 13 treads run 130 in (10 ft 10 in).
Sources
Method and figures checked on . Every worked answer on this page is covered by an automated test. Found a mistake? Tell us.