calcs.homes
calcs.homes
Enter the total rise between floors and this stair calculator works out riser height, number of risers, total run, and stringer length.
Estimate only — check local code for max riser height and min tread depth.
We divide total rise by your desired riser height and round to the nearest whole number — you can't build a fractional step. Actual riser height then redistributes the total rise evenly across that count, which usually differs slightly from what you entered. Total run multiplies tread depth by one fewer than the riser count, since the top riser lands on the upper floor rather than a new tread. Stringer length is the hypotenuse of total rise and total run, found with the Pythagorean theorem.
Riser height and tread depth aren't free choices — most building codes cap risers around 7.75 in (19.7 cm) and require at least 10 in (25 cm) of tread, because steps outside that range are a well-documented tripping hazard. Rounding to a whole riser count first, then spreading rise evenly, keeps every step in a flight the same height — inconsistent risers are one of the most common causes of stair falls, so codes and builders treat uniformity as non-negotiable.
Divide your total rise by a comfortable riser height (7-7.5 in / 18-19 cm is typical) and round to the nearest whole number — that's your riser count.
You can't have a fractional riser, so we round to a whole number of risers first, then divide the total rise evenly across them — that gives a slightly different (but consistent) riser height.
The stringer is the diagonal board that supports the treads. Its length is the hypotenuse of the total rise and total run — order lumber at least this long, plus extra for the top and bottom cuts.