QuickCheckToolsStair calculator
Enter the height from floor to floor to work out how many steps you need, each riser's height, the total run and stringer length, checked against the US residential building code (IRC).
IRC stair rules
| Rule | Requirement |
|---|---|
| Maximum riser height | 7¾ inches |
| Minimum tread depth | 10 inches (11 inches with no nosing) |
| Minimum headroom | 6 feet 8 inches |
| Minimum stair width | 36 inches |
| Variation between steps | No more than ⅜ inch within a flight |
Questions
How do I calculate the number of stairs?
Measure the total rise from finished floor to finished floor in inches and divide by the maximum riser height (7¾ inches under the IRC), rounding up. A 108-inch rise needs 14 risers of about 7 11/16 inches each.
How many treads do I need?
One fewer than the number of risers, because the top step is the upper floor. 14 risers means 13 treads.
What is the code for stair risers and treads?
The US International Residential Code sets a maximum riser of 7¾ inches and a minimum tread depth of 10 inches, or 11 inches if the treads have no nosing. Many local codes follow the IRC, but check yours.
How do I work out the total run?
Multiply the number of treads by the tread depth. 13 treads at 10 inches is a 130-inch (10 ft 10 in) run. Make sure there's room for it, plus a landing at the bottom.
How long should the stringer be?
The stringer runs diagonally, so its length is √(rise² + run²). For a 108-inch rise and 130-inch run that's about 169 inches, before allowing for cuts at each end.
Why must all steps be the same height?
Uneven steps are a major trip hazard because people expect each step to match the last. The IRC allows no more than ⅜ inch difference between the tallest and shortest riser in a flight.
Based on the International Residential Code (R311.7). Local codes and amendments vary, so confirm with your building department before you build.