Stair Stringer Calculator: 42" Total Rise

How the math works

1. Risers = 42" ÷ 7.75" max = 5.42 → round up to 6
2. Riser height = 42" ÷ 6 = 7.0000" ≈ 7"
3. Treads = risers − 1 = 5
4. Total run = 5 × 10" = 4' 2"
5. Stringer = √(42² + 50.0²) = 5' 5-5/16"

Subtract one tread thickness from the bottom riser of the stringer (drop the stringer) so the first step matches the rest.

Trade pro tips

• Measure the 42" rise from finished floor to finished floor — add flooring and tread thickness to rough measurements.
• Cut one stringer, test it in place, then trace it for the rest.
• At 36" wide, use 3 stringers; at wider than 36", add one stringer per 16"–18".

Frequently asked questions