How the stair Calculator works
Divide the total rise by your target riser height and round to a whole number of steps, then divide again for the exact riser to cut, since every riser must be equal (most codes allow only 3/8 inch variance). Treads count one fewer than risers, and the stringer is the diagonal of rise and run.
Risers = round(rise ÷ target) | Riser = rise ÷ risers | Stringer = √(rise² + run²)
Example: a 100 inch rise at a 7.5 inch target gives 13 risers of 7.69 inches, 12 treads at 10.5 inches for a 126 inch run, and a stringer just under 13.4 feet, so 14 foot stringer stock.
Frequently asked questions
What is the code for stairs?
US residential code (IRC) commonly caps risers at 7.75 inches, requires treads at least 10 inches, and limits riser variation to 3/8 inch. Local amendments differ, so confirm with your inspector.
What makes stairs feel comfortable?
The classic rule: twice the riser plus the tread should land between 24 and 25.5 inches. This calculator checks it automatically.
Why is the first riser cut shorter on the stringer?
The tread material thickness raises every step except the first, so carpenters drop the bottom of the stringer by one tread thickness to keep all finished risers equal.