Plan a safe, comfortable staircase. Enter the total rise and tread depth, and this stair calculator gives the number of steps, riser height, total run, stringer length and a diagram. It also checks the main IRC (International Residential Code) limits.
How the stair calculator works
- Total rise is the vertical distance from the finished lower floor to the finished upper floor.
- The number of risers = total rise ÷ maximum riser height, rounded up.
- Actual riser height = total rise ÷ number of risers.
- Number of treads = risers − 1 (the top floor acts as the last step).
- Total run = treads × tread depth.
- Stringer length = √(total rise² + total run²).
Example
A 108-inch (9 ft) total rise with a 7.75-inch maximum riser needs 108 ÷ 7.75 = 13.9, rounded up to 14 risers of 7.71 inches each. That gives 13 treads. With 10-inch treads, the total run is 130 inches (10 ft 10 in).
Stair code requirements (IRC, residential)
- Maximum riser height: 7¾ inches
- Minimum tread depth: 10 inches
- Riser and tread variation within one flight: no more than ⅜ inch
- Minimum headroom: 6 ft 8 in
- Minimum stair width: 36 inches
Local codes can differ from the IRC. Always confirm with your local building department before you build.
The comfort rule
A common rule of thumb is 2 × riser + tread = 24 to 25 inches. The calculator shows this value so you can adjust the tread depth for a comfortable stride.
Frequently asked questions
How many stairs do I need for 8 feet?
An 8 ft (96 in) rise needs 13 risers of about 7.38 inches with 7.75″ maximum risers.
Does the calculator include a landing?
Not yet. For stairs with a landing, calculate each flight separately using the rise of that flight.