Roof Pitch Calculator

The roof rises 6 inches for every 12 inches it travels horizontally. First number is the rise, second is the run, and the run is almost always written as 12 so pitches can be compared at a glance. A 6:12 roof and a 26.57 degree roof are the same roof described two ways.

Hold a 12-inch level flush against the roof surface, keep it level, then measure straight down from the 12-inch mark to the roof. That drop is your rise, and the pitch is that number over 12. You can also do it from the ground if you know the roof height and building width: rise is the height, run is half the width.

Under 4:12 counts as low-slope, and standard shingles often aren't rated for it. Membrane or rolled roofing takes over below that line. Between 4:12 and 9:12 is normal territory for asphalt shingles. Above 9:12 is steep enough that the labor quote climbs, because the crew needs fall protection and can't move as fast.

Because roofing is sold by actual surface area, and a sloped roof has more of it than the house it sits on. Multiply your building's footprint in square feet by the slope factor to get the real roof area, then add 10-15% for cuts and overlaps. Skip the slope factor and you'll order short, by roughly the amount the roof is steep.