Riser height is your total rise divided by the number of risers. If a 108″ floor-to-floor height is split into 15 risers, each one works out to 7.2″.
Frequently asked questions
The questions that come up most when people are laying out a stair for the first time.
The top floor acts as the final "step," so it counts as a riser but doesn't need its own tread. A stair with 15 risers has 14 treads on the way up.
The stringer is the diagonal hypotenuse of the stair's total rise and total run, found with the Pythagorean theorem: the square root of (rise² + run²).
Many residential codes call for risers no taller than about 7¾″ and treads no shallower than about 10″, though exact limits vary by jurisdiction and stair type. RiseRun flags values outside that general planning range, but always confirm against your local code.