Enter a measured rise and run to convert roof pitch into X:12 notation, degrees, and percent grade.
How to Use the Roof Pitch Calculator
Measure a rise and a run over the same span — a level and tape measure across a section of roof, or figures straight off a plan — and enter both. All three output figures update from that one ratio.
Roofers, framers, and drainage engineers each prefer a different way of expressing the same slope. A carpenter thinks in X:12, the rise in inches over a 12-inch run. A structural drawing might specify degrees instead. A civil drawing for a driveway or drainage swale almost always uses percent grade. All three describe the identical incline; this tool just moves between them.
Rise, Run, and the Tangent
The relationship falls out of basic trigonometry: slope equals rise over run, and everything else follows from that single ratio.
pitch (X:12) = (rise ÷ run) × 12
angle (degrees) = arctan(rise ÷ run)
percent grade = (rise ÷ run) × 100A 6:12 pitch, a common "medium" residential roof, works out to about 26.6° and a 50% grade — three numbers that look nothing alike but describe the exact same slope.
Reading a Roof by Eye
As a rough sanity check: anything under 4:12 reads as nearly flat and usually needs a membrane roofing system rather than shingles; 4:12 to 9:12 covers most standard asphalt-shingle roofs; past 12:12 you're into steep-slope territory where walking the roof safely requires fall protection.