Stair Calculator

Divide your total floor-to-floor rise by the maximum allowed riser height, then round up. The IRC caps residential risers at 7.75 in, so a 108 in (9 ft) rise needs ceil(108 / 7.75) = 14 risers. Actual riser height equals total rise divided by that count.

Rise is the vertical jump between steps; run is the horizontal distance between nosings. Tread depth is the actual board width, equal to run plus nosing projection minus the part overlapped by the riser below.

IRC R311.7 caps risers at 7.75 in (R311.7.5.1) and requires tread depth at least 10 in (R311.7.5.2). Handrail height is 34-38 in above the nosing line (R311.7.8.1). The calculator flags any value that breaks these limits.

Carpenters target 2 times the riser plus the tread run between 24 and 25 in. Shorter risers pair with deeper treads; taller risers with shallower ones. The IRC does not require this; the calculator shows it as advice.

Stringer length is the hypotenuse of total rise and total run. For a 108 in rise with 13 treads at 10 in (130 in run), the stringer is sqrt(108^2 + 130^2) = 169.01 in. The calculator gives geometric length only. Stringer size, count, species, grade, spacing, cuts, and connections require an approved design or qualified professional.