Stairs start with one number: total rise. Divide it into equal risers no taller than your code allows, and the rest follows.
Stair calculator
Measure total rise from finished floor to finished floor.
Enter your numbers to see the result.
How it works
- Risers = total rise / maximum riser height, rounded up.
- Actual riser height = total rise / risers. Every riser must be the same.
- Treads = risers minus 1 (the top floor is the last step).
- Total run = treads x tread depth. Stringer length is the diagonal: √(rise² + run²).
Example: 108 in of rise at a 7-3/4 in maximum needs 14 risers of about 7.71 in and 13 treads.
IRC limits (most US homes)
- Riser: 7-3/4 in maximum (R311.7.5.1).
- Tread: 10 in minimum (R311.7.5.2).
- Variation: risers and treads in one flight within 3/8 in of each other.
- Headroom: 6 ft 8 in minimum.
- Width: 36 in minimum in most cases.
The IRC is a model code; your town adopts it with its own changes. Check with your building department before you cut stringers.
Sources
- City of Boise handout on IRC Section R311.7.5, stair treads and risers
- City of Des Moines residential stairs handout (2012 IRC): headroom 6 ft 8 in, handrail 34 to 38 in
Sources last checked 1 November 2026.
Frequently asked questions
How many steps for a 9 ft rise?
108 in at 7-3/4 in maximum is 14 risers of about 7.71 in, with 13 treads.
What is the maximum stair riser height?
7-3/4 in under the IRC, with a 10 in minimum tread.
How do I measure total rise?
From the top of the finished lower floor to the top of the finished upper floor. Include flooring that is not down yet.