Roof Pitch Calculator
Enter rise and run, or the angle if you already have it, to get the pitch a roofer quotes, the angle in degrees, and the multiplier that converts a flat footprint into real roof area.
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Rise and run only have to share a unit. Measure 12 in along a level held against the roof, then the drop to the surface at the far end — that drop is your rise in a 12 run.
The area multiplier is the number that turns a flat footprint into real roof surface: a 6:12 roof carries about 12% more area than the ground it covers, and a 12:12 carries 41% more. Skipping it is the most common reason a material order comes up short.
Frequently asked questions
How do I measure roof pitch?
Hold a level horizontally against the roof surface, mark 12 inches along it, then measure straight down from that mark to the roof. That drop is the rise in a 12 inch run — a 6 inch drop is a 6:12 pitch. From inside an attic you can measure against a rafter instead, which is safer.
What does a 6:12 roof pitch mean?
The roof rises 6 inches for every 12 inches of horizontal run. It works out to a 26.6 degree angle and a 50% slope, and it carries about 12% more surface area than the footprint underneath it.
What is the minimum pitch for asphalt shingles?
Manufacturers generally rate asphalt shingles down to 2:12, and between 2:12 and 4:12 they require a double layer of underlayment. Below 2:12 you need a membrane roof rather than shingles, because water moves too slowly to shed reliably.
How does pitch change the amount of material I need?
Through the area multiplier, which is the square root of one plus the pitch ratio squared. A 6:12 roof needs about 12% more material than its footprint suggests, a 9:12 needs 25% more, and a 12:12 needs 41% more. Ordering on footprint alone is the most common way a roof order comes up short.
What is the difference between pitch, slope and angle?
They describe the same geometry three ways. Pitch is the rise in a 12 run, the way roofers quote it. Slope is that ratio as a percentage. The angle is the same thing in degrees, which is what you set a saw to.
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