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Stairs Calc

Throat

The solid wood left behind a stringer notch; keep it at least 3½ in.

The throat is the depth of solid wood remaining behind the notch of a cut stringer — the narrowest part of the board after the tread and riser triangles are removed. Too little throat and the stringer bends or snaps under load. The common rule of thumb, echoed in many jurisdictions, is to keep at least 3½ in (89 mm) of throat. Example: a 2×12 (11¼ in) with a 7½ in riser and 10 in run notch leaves roughly 5 in of throat — comfortably safe. A 2×10 might leave under 3 in, which is why deck builders default to 2×12 stringers. Measure the throat perpendicular to the cut, not vertically.

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Related terms

Stringer The notched board that carries the treads and risers; usually a 2×12. Stringer length The diagonal length of the stringer, the hypotenuse of total rise and total run. Riser height The vertical height of a single step; every riser must be equal within 3⁄8 in.

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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.