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Stairs Calc

Stringer mount (standard vs flush)

Whether the top tread sits one riser below, or level with, the upper floor.

Stringer mount describes how the top of the staircase meets the upper floor. With a standard mount, the top tread sits one riser below the upper floor, so the floor itself acts as the last step. With a flush mount, the top tread is level with the upper floor. The choice changes the cut layout and the stringer length but not the riser height. Example: for 14 risers, a standard mount cuts 13 tread notches; a flush mount cuts 14. Getting this wrong is the classic stringer mistake — you end up with a final step that is too tall or too short, violating the 3⁄8 in uniformity rule.

Try the calculator Stair Stringer Calculator

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. Tread The horizontal board you step on; its depth equals the run plus the nosing. Plumb cut & seat cut The vertical and horizontal end cuts that let a stringer meet the floors.

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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.