Stair Calculator

Getting a staircase right comes down to three measurements working together: riser height, tread depth, and stringer length. Enter your total rise and run, and the calculator works out each value so that every step lands at the same slope, the foundation of a stairway that feels natural underfoot and passes inspection on a renovation or new build.

The math here follows the International Residential Code limits: risers no taller than 7.75 inches, treads at least 10 inches deep, and at least 6 feet 8 inches of headroom measured straight up from the line of the stair nosings (IRC R311.7). With your total rise and run in hand, the tool applies basic trigonometry to derive the stringer length, holding the angle constant across the full run so no single step feels off.

Local jurisdictions sometimes tighten these IRC figures, so confirm what your building department enforces before you cut lumber. Landings deserve the same attention as the steps themselves: keep each one at least as wide as the stairway and no less than 36 inches deep in the direction of travel. Skip that and you invite both failed inspections and a real tripping hazard. Beyond riser, tread and width, the IRC also caps a single flight at 12 feet 7 inches (151 inches) of rise between floors or landings (R311.7.3), requires a 3/4 to 1 1/4 inch nosing on treads shallower than 11 inches (R311.7.5.3), and requires a handrail 34 to 38 inches above the nosings on any flight with four or more risers (R311.7.8), so check those on your plan as well.