Understanding and Calculating Roof Pitch

Written by: Sean Summers, National Fireplace Institute (NFI) Master Hearth Certified Technician - WoodStovePro.com

Roof pitch is simply a numerical expression of the steepness of a roof. In the U.S., this is usually represented by a fraction in which the numerator signifies the rise and the denominator the run. For example, if we have a roof that rises 4 inches over 12 inches of run, then we would denote it as a 4/12 pitch. Pitch can also be expressed in degrees and discussed as an angle (see Figure 1).

The calculation of pitch is fairly simple. If you have two tape measures, or rulers, you can find the pitch from the rooftop or inside your attic space. Refer to Figure 2 to see how to arrange your tools for measuring pitch.

Please remember to be cautious when working on your roof or unfinished attic space. If you still have questions, please leave a comment or send us an email. We are always happy to help.