Stair Calculator
Work out the number of steps, the exact riser height, the tread run and the total run from your total rise.
How it works
risers = round(total rise ÷ target riser) · actual riser = total rise ÷ risers · total run = (risers − 1) × tread run
The total rise must divide into equal risers, so dividing by a target height and rounding to a whole number sets the step count; the actual riser height is then the total rise split evenly among them. There is always one fewer tread than riser (the top floor is the last “tread”), and the total run is the treads times each tread’s depth. Equal risers are what make a stair feel safe underfoot.
Worked example
A 108 in floor-to-floor rise with a 7 in target: 108 ÷ 7 = 15.4, rounded to 15 risers of 7.2 in each. That gives 14 treads; at 10 in deep the stair runs 140 in, or about 11.7 ft.
Frequently asked questions
What are the code limits for stairs?
The common US residential rule (IRC) caps risers at 7-3/4 in and requires treads of at least 10 in, with no more than 3/8 in variation between steps. Commercial codes are stricter. Always confirm your local adoption before cutting stringers.
What is a comfortable stair?
Carpenters use “rise + run ≈ 17–18 in” or “2 × riser + tread ≈ 24–25 in” as comfort rules. A 7 in riser with an 11 in tread is a classic, easy-climbing combination.
Why must every riser be equal?
People climb stairs on autopilot; a single riser even 1/2 in off is a trip hazard and a code violation. Splitting the total rise into equal parts — never leaving an odd short step at top or bottom — is the whole point of the math.
Related calculators
Estimates only — add for waste and confirm against local building codes and supplier specs.