Stair Calculator

Divide the total rise by your preferred riser height and round to a whole number of risers, then divide back for the exact riser. A 106 in (2,700 mm) floor-to-floor with a 7 in (175 mm) target gives 106 ÷ 7 ≈ 15 → 15 risers of exactly 7.09 in (180 mm). The number of treads is one fewer than the risers, and total run = treads × tread depth.

The classic comfort rule: twice the riser plus the tread depth should land between 24 and 25½ in (600–650 mm) — 2R + T. A 7 in (180 mm) riser with a 10 in (250 mm) tread gives 24 in (610 mm) — comfortable. Residential stairs typically run 6–7½ in (150–190 mm) risers and 9½–12 in (240–300 mm) treads; public buildings are stricter.

Because feet learn the rhythm on the first two steps — a single odd riser, even ⅜ in (10 mm) off, is the most reliable trip hazard in a building, and building codes (the IRC) limit the variation between risers to ⅜ in (about 10 mm). Set out from finished floor levels on both floors, remembering underlayment and finishes change the first and last rise.

Comfortable stairs land between about 30° and 38°; the calculator shows your angle from the riser and tread depth (angle = atan(riser ÷ tread)). Steeper than about 42° feels like a ladder and usually fails residential codes; shallower than 25° wastes floor space and trips people who expect a normal pitch.

Typical US limits (IRC): maximum riser 7¾ in (196 mm) and minimum tread depth 10 in (254 mm) for houses, at least 6 ft 8 in (2,030 mm) of headroom over the pitch line, a maximum number of risers per straight flight before a landing, and handrail heights. These vary by jurisdiction — check your local code before cutting stringers.