A worked example
A 108-inch total rise with a 7-inch target riser comes to exactly 15 risers at 7.2 inches each, with 14 treads.
Frequently asked questions
Why does the actual riser height differ from my target?
The number of risers has to be a whole number, so the total rise gets divided evenly across that whole number of steps — the result is usually close to, but not exactly, your target riser height.
Why is the number of treads one less than the number of risers?
Each riser represents a vertical step up; the top step lands you on the upper floor itself, which doesn't need its own tread — so a staircase with 15 risers only has 14 actual tread surfaces.
What's the stringer length used for?
It's the length of lumber needed for the diagonal support boards that the treads and risers attach to — knowing this length helps you buy the right size stock before cutting the stair stringers.
Always confirm your local building code's specific riser, run, and headroom requirements before building — they vary by jurisdiction.