stair calculator
Enter the floor-to-floor height and get the number of steps, riser height, tread depth, total run, stringer length and angle. Each result is checked against common building-code limits.
fashion law journal · tools deskupdated 25 sep 2026IRC & UK Part K checks
Quick answer: divide the total rise by a target riser height of about 7 inches and round up to get the number of risers. Then divide the rise by that number for the exact riser height. You’ll have one fewer tread than risers. For a 108-inch rise, that’s 16 risers of 6¾ inches and 15 treads.
Total rise is finished floor to finished floor. Measure it after flooring, or add the flooring thickness.
stair building code limits
| rule | US (IRC, homes) | UK (Part K, private stair) |
|---|---|---|
| Maximum riser | 7¾ in (197 mm) | 220 mm |
| Minimum tread (going) | 10 in (254 mm) | 220 mm |
| Maximum pitch | not set directly | 42° |
| Minimum headroom | 6 ft 8 in (2,032 mm) | 2,000 mm |
| Riser variation | max ⅜ in between steps | all steps equal |
The IRC is the model code most US states and cities adopt, often with local amendments. Commercial buildings follow stricter rules (the IBC, with a 7 in maximum riser and 11 in minimum tread). Always confirm with your local building department before you build.
the comfortable-stair rule
Stairs feel natural when twice the riser height plus the tread depth adds up to 24 to 25 inches (600 to 640 mm in the UK rule). A 7-inch riser with a 10½-inch tread gives 24.5. Very tall risers with shallow treads feel steep, and very short risers with deep treads feel awkward.
stair questions
How many steps do I need for a 9 ft ceiling?
With a typical 9 ft ceiling and floor structure, the total rise is often around 108 to 112 inches. That needs 15 or 16 risers at 7 to 7½ inches each. Measure your actual rise.
How do I calculate stringer length?
Stringer length is the hypotenuse of the total rise and total run: √(rise² + run²). Add a little for the cut at the top and bottom.
What is the standard stair riser height?
Around 7 to 7½ inches in homes. The US residential maximum is 7¾ inches, and 220 mm for UK private stairs.
Do I need a permit to build stairs?
For interior stairs and most decks, usually yes. Requirements vary by city and county, so check with your building department first.
A planning tool, not a substitute for local code review or an engineer. Codes are amended locally. Not legal advice. More tools: square footage calculator · cubic yard calculator.