Stair Calculator
Enter the total rise from floor to floor. For a 108 inch rise the calculator gives 14 steps with a riser of 7.714 in inches.
How stairs are calculated
Divide the total rise by your target riser height and round to the nearest whole number to get the number of steps. Then divide the total rise by that number for the exact riser height. A staircase always has one fewer tread than risers because the top floor acts as the last tread.
With a rise of 108 inches and a 7.5 inch target, you get 14 risers of 7.714 in inches. Total run is treads x tread depth, and the stringer length comes from the Pythagorean theorem: the square root of rise squared plus run squared.
Building code basics
- The International Residential Code limits risers to 7.75 inches and requires treads of at least 10 inches.
- All risers in one flight should be within 3/8 inch of each other.
- Rule of thumb: 2 x riser + tread should be between 24 and 25 inches for comfort.
Codes vary by city, so confirm with your local building department before cutting stringers.
Free pricing tips for your business
Get short, practical tips on pricing jobs and using our free calculators. No spam, unsubscribe any time.
Frequently asked questions
How do I calculate the number of stairs?
Divide the total rise by the riser height you want (about 7 to 7.75 inches) and round to the nearest whole number.
What is the maximum riser height?
The US residential code allows a maximum of 7.75 inches. Commercial stairs are usually limited to 7 inches.
How long should a stair stringer be?
Stringer length is the square root of total rise squared plus total run squared. The calculator shows it for your numbers.
What is a comfortable stair angle?
Between about 30 and 37 degrees. Steeper than 40 degrees feels like a ladder.
Need a custom calculator or spreadsheet built for your business?
Talk to usMore free tools: All free calculators · Roof pitch calculator · Deck calculator · Square feet calculator