Roof pitch calculator

How pitch is worked out

Pitch compares how far a roof climbs (the rise) with the level distance it covers (the run). In the US and Canada it is written as a rise in 12: a roof that climbs 6 in over 12 in of run is a 6 in 12 pitch, also written 6/12. In the UK and Australia it is usually given in degrees.

• x in 12 = rise / run x 12.
• Angle = arctangent(rise / run), in degrees.
• Percent grade = rise / run x 100.
• Slope factor = √(rise² + run²) / run. Multiply a level distance by it to get the length along the slope.

Worked example

Rise 6, run 12: 6 / 12 x 12 = 6 in 12. The angle is arctan(0.5) = 26.57°. The grade is 50%. The slope factor is √(36 + 144) / 12 = 1.118, so a rafter that covers 12 ft of level run is 13.42 ft long along its top edge, before any overhang or cut at the ridge.

Measuring

Use any unit, but the same one for both. For a simple gable the run is half the building's width. A 45° roof is 12 in 12.

What it does not tell you

The lowest pitch a roofing product allows is set by its maker, and rafter sizes and spans are set by the local code. This page converts measurements only. For roof area and shingle bundles, use the roofing calculator.