Q. How do I calculate the pitch of a roof?
A. Roof pitch is a numerical measure of the steepness of a roof. The roof’s pitch is the measured vertical rise divided by the measured horizontal span or run. It is the same thing as what is called “slope” in geometry. The purpose of a pitched roof is to redirect rain or snow. In the United States, slope is typically given in inches per 1 foot, or as a ratio of inches per 12 inches, and commonly referred to with units of “pitch.” For a roof slope of 1/3, a “4 pitch” roof indicates 4 inches of rise over 1 foot of run; a “4:12 pitch” is 4 inches of rise over 12 inches of run. You can calculate roof pitch with the following formula: Roof pitch = (rise/run)x12.