Stair anatomy — total rise, riser, tread, and run, and how rise sets the number of steps

What this diagram shows

A side elevation of a stair flight labeling the parts of stair geometry. The total rise is the vertical distance from finished floor to finished floor; the total run is the horizontal distance the stair covers; one riser is the height of a single step (about 7¼ inches) and one tread is its depth (about 11 inches). The number of risers equals the total rise divided by the maximum 7¾-inch riser, rounded up; the number of treads is one less than the risers; and the total run is the tread count times the tread depth. For a 9-foot (108-inch) floor-to-floor that is 15 risers at 7.2 inches, 14 treads at 11 inches, and a 154-inch run. Every riser in a flight must be equal.