Roof pitch describes how steep a roof is — in the US as inches of rise per 12 inches of run (for example 6/12), and elsewhere usually in degrees. Enter a rise and run, or an angle, to convert between pitch, degrees and slope percentage.
Formula
Pitch = Rise ÷ Run × 12 · Angle = arctan(Rise ÷ Run)
The pitch factor √(1 + (Rise ÷ Run)²) converts a horizontal area or run into the actual sloped length or area.
Worked example
A roof that rises 6 inches for every 12 inches of run has a 6/12 pitch, an angle of 26.57° and a 50% slope. Its pitch factor is 1.118, so a 1,000 ft² footprint has about 1,118 ft² of roof.
Common pitches
Low slope: below 4/12 (18.4°) — needs special roofing. Conventional: 4/12 to 9/12. Steep: above 9/12 (36.9°). Most asphalt shingles need at least 2/12, with extra underlayment below 4/12.
Frequently asked questions
What angle is a 4/12 roof pitch?
About 18.43°. A 6/12 pitch is 26.57°, an 8/12 pitch is 33.69° and a 12/12 pitch is 45°.
How do I measure roof pitch?
Hold a level horizontally against the roof (or rafter), measure 12 inches along it, then measure straight down to the roof surface. That vertical distance is the rise per 12.
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