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Stairs Calc

Stringer length

The diagonal length of the stringer, the hypotenuse of total rise and total run.

Stringer length is the straight-line diagonal of the staircase — the hypotenuse of a right triangle whose legs are the total rise and the total run. It tells you how long a board to buy before cutting notches. Example: a 105 in rise and 130 in run gives √(105² + 130²) ≈ 167 in (4.24 m), so you need at least 14 ft stock plus waste for the plumb and seat cuts. The unnotched throat line is what actually bears load, so order a board longer than the bare hypotenuse. No code dictates length; it is pure geometry, which is why the stringer calculator solves it exactly.

Try the calculator Stair Stringer Calculator

Related terms

Stringer The notched board that carries the treads and risers; usually a 2×12. Throat The solid wood left behind a stringer notch; keep it at least 3½ in. Total run The horizontal distance the whole flight covers, floor to floor. Stair angle (pitch) The slope of the flight in degrees; comfortable stairs sit around 30–37°.

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Stair Stringer Calculator Get the exact stringer length, throat depth, recommended board size, and a step‑by‑step cut layout with framing‑square settings — then print a full‑scale template.
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Written by the Stairs Calc editorial team. Methodology and code references: see our methodology.

Built and maintained by builders, drafters and engineers who plan stairs for a living — every code limit is transcribed from the published standard and cited to its exact section.

Last reviewed 2026-06-20 against IRC 2021/2024

Stairs Calc gives accurate geometry and checks it against published building-code limits, but results are estimates for planning. Codes are adopted and amended locally and change over time. Always confirm dimensions against your local adopted code and a licensed professional before you build.