How this stair calculator works
Divide the total rise — finished floor to finished floor — by your target riser height and round up to a whole number of risers. The actual riser height is then the rise divided by that count, so every step is identical; uneven steps are the number one trip hazard on stairs. Treads are always one fewer than risers, the total run is treads times tread depth, and the stringer is the diagonal of rise and run.
Code limits to know
US residential code (IRC) caps risers at 7¾ inches (196 mm) and requires treads at least 10 inches (254 mm) deep, with no more than ⅜ inch variation between steps. Many European codes cap risers around 18–19 cm. The classic comfort rule: two risers plus one tread should land between 24 and 25 inches (61–64 cm).
Measure the rise honestly
Measure from finished floor to finished floor — including any flooring not yet installed on either level. A ¾ inch oversight at the top becomes one step that is ¾ inch off, which is exactly the step people trip on. For deck stairs, measure from the pad or footing where the stringer lands, and slope that pad away from the structure.