Stair Calculator

Total rise is the vertical distance from one finished floor to the next. Divide it by a target riser height (7.5 in is a common starting point) and round to a whole number of risers — you can't have a fraction of a step. That gives you the actual riser height, which should land close to your target once you divide the rise evenly.

The number of treads is one less than the number of risers, because the top floor itself counts as the last "step." Multiply tread depth by tread count to get total run, then add any run for a landing. The stringer — the diagonal board the treads sit on — is the hypotenuse of the rise and run, found with the Pythagorean theorem.

For deck stairs, run this the same way using the deck's height above grade as the total rise; tread depth is often 11 to 11.25 in outdoors since deck boards are wider than indoor treads.

Where these numbers come from

These are planning estimates. Check product labels, your local building code, and a licensed contractor before you buy materials or build.