Key Takeaways
- The same roof slope can be written as a pitch, an angle or a percent grade
- A 6 in 12 pitch is about 26.6 degrees and a 50 percent grade
- A 12 in 12 pitch equals 45 degrees and a 100 percent grade
- Different trades and documents default to different notations
A single roof slope has three common names, and which one you need depends on who is asking. A framer’s plan might specify pitch in x-in-12 notation. A solar panel installation guide might ask for degrees. A drainage or civil engineering calculation might use percent grade. They are all the same number, expressed differently.
Pitch to degrees and percent
Pitch, written as x in 12, is the ratio of rise to a 12 inch run. Divide the pitch number by 12 to get that ratio, then take the arctangent to get the angle in degrees, or multiply by 100 to get the percent grade. A 6 in 12 pitch: 6/12 = 0.5, arctangent of 0.5 is about 26.6 degrees, and 0.5 x 100 is a 50 percent grade.
Degrees to pitch and percent
Working from an angle, take the tangent of the angle to get the rise-to-run ratio, then multiply by 12 for pitch or by 100 for percent grade. A 45 degree angle: tangent of 45 degrees is 1, so that is a 12 in 12 pitch and a 100 percent grade, an unusually steep roof; most residential roofs fall between about 4 in 12 and 9 in 12.
Percent to pitch and degrees
From a percent grade, divide by 100 to get the ratio, then multiply by 12 for pitch or take the arctangent for the angle. A 25 percent grade: 25/100 = 0.25, which is a 3 in 12 pitch and about 14 degrees.
Why this differs from measuring pitch directly
If you are standing at the roof with a level and a tape measure, the roof pitch calculator is the more direct tool: it takes a measured rise and run and gives you pitch, angle and percent together. This conversion is for the opposite situation, when a document, spec sheet or another calculation already states a slope in one notation and you need it translated to another.
Use the roof slope calculator to convert between pitch, degrees and percent grade directly. Once you have a pitch, the roof square footage calculator turns a building footprint and that pitch into actual roof surface area.