Stair Calculator
Work out how many steps a staircase needs, each step's height, the total run and the angle, with a check that the stairs will be comfortable to climb.
About 7 inches (18 cm) is comfortable for homes; building codes often allow up to 7.75 inches.
The flat part you step on. 10 to 11 inches (25 to 28 cm) is usual.
Steps (risers)
18
- Each step's height
- 6.6667 in
- Total run (length)
- 187 in for 17 treads
- Angle
- 31.2184 °
- Comfort check
- 24.3 in stride: comfortable
A 120 in rise needs 18 steps of 6.67 in, with 17 treads of 11 in: 187 in of run at 31.2°, which is comfortable.
How it's worked out
- Number of steps
120 ÷ 7, rounded up18 - Step height
120 ÷ 186.67 in - Run
17 treads × 11 in187 in - Steepness
step 6.67 in (most 7.75), tread 11 in (least 10)within limits - Stride rule
2 × riser + tread should be about 24 to 25.5 inches (61 to 65 cm)24.3 in
- Building codes set limits on step height, tread depth, headroom and handrails. Check your local rules or with your architect.
The formulas
Risers = total rise ÷ highest step, rounded up · Treads = risers − 1 · Comfort: 2 × riser + tread ≈ 24 to 25 inches
Worked example
A 120-inch rise with steps no higher than 7 inches needs 18 risers of 6.67 inches. With 11-inch treads, the 17 treads take 187 inches of floor at about 31°, and 2 × 6.67 + 11 = 24.3 inches: comfortable.
Questions people ask
How many steps do I need for a 10-foot ceiling?
A 120-inch floor-to-floor height with steps up to 7 inches needs 18 steps of 6.67 inches.
What is a comfortable step size?
A step height of about 6.5 to 7.5 inches with a tread of 10 to 11 inches. A good check is that twice the step height plus the tread comes to about 24 to 25 inches.
How many treads are there?
One fewer than the number of risers, because the top step is the floor above.
About this calculator
Formula and rules last checked 25 October 2026Written and tested by the CalculatorDex teamReport a problem