How the stringer calculator works
Two numbers from one layout
Stringer length is the hypotenuse of total run × total rise (the slope you walk). Board width is the catch: the cut teeth must leave enough wood — rise + tread's diagonal + margin ≈ the stock depth needed. An 11¼-in 2×12 carries typical residential layouts; a 2×10 fails layouts with tall risers, and the calculator says so before the lumber yard does.
How many stringers
Three for 36-inch stairs (one per end, one centered), four for 48-inch, and treads never span more than ~16 inches unsupported — the "3-pound ball" deflection test inspectors apply by eye. Wider stairs: add stringers proportionally.
The cutting discipline
- Cut one layout stringer from straight, crown-up stock — use the layout calculator's numbers, framed square.
- Test-fit it before cutting the rest: total rise to finished floor, headroom at the top.
- Clamp, trace, cut the rest — never re-measure; the template IS the tolerance.
- Leave the last teeth deep: over-notching the bottom weakens the seat — notch to the layout line, not past it.