Stair Stringer Calculator

Calculate stair stringer length, riser count, tread dimensions, and lumber for building stairs.

📏 Stair Stringer Calculator

Results

Number of Risers5
Actual Riser Height7.20 in
Number of Treads4
Total Run40.00 in
Stringer Length4.5 ft
Stringers Needed3

💡 How to Calculate Stair Stringers

A stair stringer is the diagonal board that supports the treads and risers. The number of risers equals total rise divided by desired riser height (rounded to the nearest whole number). Treads = risers minus 1. Stringer length is calculated using the Pythagorean theorem: √(total rise² + total run²).

Building code requires risers between 4–7.75 inches (7–7.5 inches is ideal) and treads at least 10 inches deep. All risers must be within 3/8 inch of each other. Use 2×12 lumber for stringers, as the notched throat depth must be at least 3.5 inches.

A 36-inch total rise with 7.5-inch risers: 5 risers, 4 treads at 10 inches = 40-inch run. Stringer length = √(36² + 40²) / 12 = 4.5 ft. Use 2×12 × 6 ft lumber.

Stair Stringer Calculator FAQ

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