How stair stringer calculator works
Every stair starts with one measurement: total rise, the floor-to-floor (or deck-to-grade) height the stairs must climb. Divide it by your target riser height — 7 inches is the classic target, and codes cap risers near 7¾ inches — then round up to a whole number of risers. The actual riser is total rise ÷ riser count: splitting a 106 in rise into 16 risers gives 6.63 inches each.
Treads follow from the count: a stair with N risers has N − 1 treads, because the upper floor itself is the last 'tread'. Total run is treads × tread depth — 10 inches is the common minimum with nosing. Rise and run together set the stringer: its length along the slope is the hypotenuse, √(run² + rise²), and the stair angle is atan(rise ÷ run). Comfortable stairs sit near 30–37 degrees.
The tool also checks the classic comfort rule: 2 × riser + tread should land between about 24 and 25.5 — a 7 in riser with a 10 in tread scores exactly 24. Below that range stairs feel shallow and stuttery; above it they feel steep. It's a design heuristic rather than code, so always verify local rise, run, nosing and headroom rules before cutting — and remember the first stringer you cut becomes the template for all the rest.