Stair Calculator

Building codes typically require 7-7.75 inch rise (max) and 10-11 inch run (min). The comfort formula 2R + T = 24-25 inches ensures comfortable climbing. For example: 7" rise + 11" tread = 25" (ideal).

Divide total rise (floor-to-floor height) by desired rise per step. For 9-foot ceiling (108 inches): 108 ÷ 7.5 = 14.4, round to 14 steps. Then recalculate: 108 ÷ 14 = 7.71 inches per step.

Headroom is the vertical clearance from the nosing to any obstruction above. Minimum is 6'8" (80 inches). Insufficient headroom is a code violation and safety hazard. Consider headroom when planning stair openings.

Use the Pythagorean theorem: length = √(total rise² + total run²). For a stair with 9 ft rise and 12 ft run: √(81 + 144) = √225 = 15 feet stringer length. Add extra for top and bottom cuts.

IRC/IBC codes require: max 7.75" rise, min 10" tread depth, min 36" width, max 12 risers between landings, 6'8" min headroom, and handrails on one side. Local codes may be stricter.

Residential stairs minimum 36 inches, commercial 44 inches. Main stairs in homes are often 42-48 inches for comfort. Measure clear width between handrails or walls, not including the handrails themselves.