Definition
Pitch is the slope or incline of a roof, expressed as the ratio of vertical rise to horizontal run. In the US, pitch is typically written as X:12, where X is inches of rise per 12 inches of horizontal run. For example, a 6:12 pitch rises 6 inches vertically for every 12 inches horizontally. Pitch affects roofing material selection, drainage, attic space, and installation complexity. Flat roofs have pitches under 2:12, low slopes are 2:12-4:12, and steep roofs exceed 12:12.
Formula
To calculate pitch: Measure the vertical rise over a 12-inch horizontal distance. Alternatively, divide total rise by total run and multiply by 12. A roof that rises 8 feet over a 24-foot span has an 8:24 pitch, which equals 4:12 (8 / 24 x 12). Pitch in degrees = arctan(rise/run) x 180/pi.
Example
Roof Pitch Example
A 4:12 pitch roof rises 4 inches for every 12 inches horizontally (approximately 18.4 degrees). This is a common low-slope pitch suitable for asphalt shingles. Steeper pitches like 8:12 (33.7 degrees) or 12:12 (45 degrees) shed snow and water more effectively but require more materials and safety equipment for installation.