Calculators/ Roofing/Roof Pitch Calculator
Roof Pitch Calculator
Convert roof pitch to angle, slope and area multiplier.
Roof Pitch Calculator
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Roof pitch is written as rise over a 12 inch run, but you often need it as an angle for a saw, as a multiplier for area, or as a percentage for drainage. This converts between all of them.
How this is calculated
- The angle is arctan(rise ÷ run), converted from radians to degrees.
- The area multiplier is √(1 + (rise÷run)²). Multiply any horizontal area by this to get the sloped surface area.
- Common rafter length is half the span times the multiplier, before adding the overhang and subtracting half the ridge board thickness.
Frequently asked questions
What is the minimum pitch for asphalt shingles?
2/12 is the absolute minimum and requires a doubled underlayment. Most manufacturers want 4/12 or steeper for a standard warranty.
What pitch is 45 degrees?
A 12/12 pitch, where the rise equals the run. Its area multiplier is 1.414, so the roof surface is 41% larger than the footprint.
Is pitch the same as slope?
In roofing they are used interchangeably, both meaning rise over run. In civil engineering slope usually means a percentage grade instead.