Stair width
The clear walking width of the flight; IRC minimum 36 in above the handrail.
Stair width is the clear walking space across the flight, measured between the walls or guards. It governs how easily two people pass and whether furniture fits. The IRC requires a minimum 36 in (914 mm) clear width above the handrail, with the handrail allowed to project no more than 4½ in into that space on each side. The IBC and OSHA set wider minimums for commercial and egress stairs based on occupant load. Example: a 36 in stair with one wall-mounted handrail keeps about 31½ in of clear passage. Wider stairs over 36 in usually need a stringer added under the center of the treads to prevent bounce.
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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.