Stair Calculator
Find the number of steps, riser height, total run, stringer length and angle for a stair from its total rise, checked against IRC limits.
Change the values and press Calculate to work out your own figures.
From the largest riser
Enter the total rise and, optionally, the largest riser and the tread depth.
Show the working
- risers = ⌈total rise ÷ largest riser⌉
- riser = total rise ÷ risers; run = (risers − 1) × tread
From the number of risers
Enter the total rise and the number of risers.
Show the working
- risers = ⌈total rise ÷ largest riser⌉
- riser = total rise ÷ risers; run = (risers − 1) × tread
How to use it
Enter the total rise and, optionally, the largest riser and the tread depth. Enter the total rise and the number of risers.
Lengths can be decimals, fractions or tape entries such as 12' 6 1/2" (in feet or inches). Prices are optional.
Key facts
risers = ⌈total rise ÷ largest riser⌉; riser = total rise ÷ risers treads = risers − 1; run = treads × tread depth; stringer = √(rise² + run²)
Code
The IRC allows risers up to 7 3/4 in and treads at least 10 in deep, varying by no more than 3/8 in, with 6 ft 8 in of headroom and stairs at least 36 in wide. Local codes may differ.
Questions
How many steps for a 9 ft rise?
14 risers of about 7 11/16 in (7.71 in), with 13 treads.
Formulas
risers = ⌈total rise ÷ largest riser⌉; riser = total rise ÷ risers treads = risers − 1; run = treads × tread depth; stringer = √(rise² + run²)
Sources
Limitations
- Material densities are typical values (the midpoint of the commonly published range); real loads vary with moisture, grading and compaction, so check with your supplier or type in their density.
- Tank results are the geometric volume; real tanks have wall thickness and fittings.