How to use the stair calculator
- 1 Enter the total rise, floor to floor, in inches.
- 2 Enter the maximum riser height you want (7¾ inches or less for homes).
- 3 Enter the tread depth and the stair width.
- 4 Read the risers, treads, run, stringer length and code check.
Worked example
A total rise of 108 inches (9 feet) with risers of 7.5 inches or less and 10.5-inch treads. That needs 15 risers of 7.2 inches and 14 treads, a total run of 147 inches (12.25 feet). The stringer is about 182.4 inches (15.2 feet) long, the angle is 36.3°, and 2 × 7.2 + 10.5 = 24.9 inches meets the comfort rule.
Building stairs that feel right
- Keep every riser equal: uneven steps cause trips.
- Measure to finished floors.
- Aim for 2R + T of 24 to 25 inches.
- Check local code before you build.
Pour a landing with the Concrete Calculator, check angles with the 30-60-90 Triangle Calculator, and convert with Feet to Meters. Order gravel for a path at the bottom with the Gravel Calculator.
How it works: The total rise is divided by your maximum riser height and rounded up to get whole steps, so every riser is equal and no taller than your limit. Treads are one fewer than risers, and the stringer length comes from the Pythagorean theorem on the rise and run.
Features
Exact riser height
Equal risers that add up to the total rise.
Stringer length
Run, rise and angle for cutting stringers.
Code and comfort check
IRC limits and the 2R + T rule.
When to use it
Deck stairs
Plan steps from a deck to the yard. Pour a landing pad with the Concrete Calculator.
Basement stairs
Lay out a staircase between floors.
Angles
Check the angle with the 30-60-90 Triangle Calculator.
Measuring
Convert inches and feet with the Feet to Meters converter.
Related Construction tasks
Frequently asked questions
How do you calculate stairs?
Divide the total rise by the maximum riser height and round up to get the number of risers. Divide the rise by that number for the exact riser height. Treads are one fewer than risers; the run is treads × tread depth.
How many steps for 9 feet?
108 inches of rise with risers of 7.5 inches or less needs 15 risers of 7.2 inches and 14 treads.
What is the maximum riser height?
7¾ inches under the International Residential Code for homes. Commercial stairs are usually limited to 7 inches.
What is the minimum tread depth?
10 inches under the IRC for homes, measured from the edge of one tread to the edge of the next; 11 inches for most commercial stairs.
What is the 2R + T rule?
Two risers plus one tread should equal 24 to 25 inches for a comfortable stride. 7.2 + 7.2 + 10.5 = 24.9 inches.
How do I measure total rise?
Measure from the top of the lower finished floor to the top of the upper finished floor. Include flooring thickness on both levels.
How long is a stair stringer?
About √(rise² + run²), plus extra at the top and bottom for cuts and attachment. Buy boards a little longer.
What angle should stairs be?
Most home stairs are between 30° and 37°. Steeper than about 42° feels like a ladder.
How wide should stairs be?
At least 36 inches clear width under the IRC for homes.
Do I need a handrail?
Under the IRC, stairs with four or more risers need a handrail between 34 and 38 inches high. Check your local code.
What is a stair stringer?
The sloped board that supports the treads and risers on each side of the stairs.
What is nosing?
The front edge of a tread that sticks out past the riser below, usually ¾ to 1¼ inches under the IRC.
Built and reviewed by Hamza Farooq, founder and lead developer
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