Slope and roof pitch calculator

How to use the Slope & Roof Pitch

Convert a roof or ramp slope between degrees, percent, a 1 : n ratio and the x-in-12 pitch used in the US, and get the rise and rafter length for a given run.

1. Choose what you know: rise and run, an angle, a percentage, an x-in-12 pitch or a 1 : n ratio.
2. Enter the value and the horizontal run.
3. Read the slope in every format, the rise over the run and the rafter or slope length.

Worked example

A rise of 1.5 m over a 4 m run is a 20.56° slope, 37.5%, a 4.5-in-12 pitch or 1 : 2.67. The rafter (slope length) is 4.272 m before any overhang.

Good to know

• Percent slope is rise ÷ run × 100, so a 45° slope is 100%.
• Roofing materials have minimum pitches; check the manufacturer before choosing a low slope.
• Add the eaves overhang to the rafter length when ordering timber.