Calculate stair stringer length, rise, run, number of steps, and stringer angle. IRC code compliance for residential stairs.
Enter the total rise — the finished floor-to-floor height in inches — and your tread depth. The calculator divides the rise by a 7.5 inch target riser and rounds to the nearest whole number (minimum two) to set the riser count, then computes the exact riser height each step must use.
Total run is (risers − 1) × tread depth, because the top riser lands on the upper floor rather than a tread. For a 105 inch rise with 10 inch treads you get 14 risers of exactly 7.5 inches, a 130 inch run, a stringer length of √(105² + 130²) ≈ 167.1 inches, and a 38.9° stair angle.
The comfort check uses the 2R + T rule: twice the riser height plus the tread depth. The calculator marks the result as passing when it falls between 24 and 26 inches — the 7.5 inch riser with a 10 inch tread scores exactly 25.
A classic ergonomic check: twice the riser height plus the tread depth should land between 24 and 26 inches — the range this calculator marks as passing. A 7.5 inch riser with a 10 inch tread scores exactly 25, right in the comfortable middle.
Total rise ÷ 7.5 inches, rounded to the nearest whole number with a minimum of two. The actual riser is then total rise ÷ count so every step is identical — a 100 inch rise yields 13 risers of about 7.69 inches each.
The final riser steps onto the upper floor itself, so a stair with n risers has n − 1 treads. Fourteen risers with 10 inch treads therefore need only 130 inches of horizontal run, which is the distance the stringer must cover.
The stringer length is the hypotenuse of the rise-run triangle: √(rise² + run²). A 105 inch rise over a 130 inch run needs about 167 inches — just under 14 ft — measured tip to tip before any plumb or level cuts are marked.