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Stairs Calc

Tread

The horizontal board you step on; its depth equals the run plus the nosing.

The tread is the physical board your foot lands on. Its depth is the run plus the nosing overhang, so a 10 in run with a 1 in nosing produces an 11 in (279 mm) tread board. Tread thickness matters structurally: a 1 in nominal pine tread spans differently than a 2× lumber tread, and wider stairs may need a center stringer to stop bounce. Example: a 36 in wide residential stair in softwood typically wants three stringers so the tread does not deflect. Codes regulate the run and nosing rather than the board itself, but a slip-resistant surface is required on commercial and outdoor treads.

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Related terms

Run (going) The horizontal depth of one step, measured nosing-to-nosing, not counting the overhang. Nosing The lip of the tread that overhangs the riser below; ¾–1¼ in in the IRC. Riser (board) The vertical board that closes the gap between two treads on a closed-riser stair. Stringer The notched board that carries the treads and risers; usually a 2×12.

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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.