How to use the Roof Pitch Calculator
- 1
Hold a level horizontally against the roof and measure 12 inches along it (the run).
- 2
Measure straight up from the 12-inch mark to the roof surface (the rise) and enter both numbers.
- 3
Read the pitch, angle and multiplier. Add the building span to get the rafter length.
Roof pitch, slope and angle
Roof pitch is written as rise over a 12-inch run: a 6/12 roof rises 6 inches for every 12 inches across. The angle is the arctangent of rise ÷ run, so 6/12 is 26.6°. Slope as a percentage is rise ÷ run × 100, so 6/12 is a 50% slope.
The pitch multiplier is √(1 + (rise ÷ 12)²). Multiply the flat footprint of a roof by it to get the real surface area. A 6/12 roof has a multiplier of 1.118, so a 1,500 sq ft footprint is about 1,677 sq ft of roof.
What pitch means for roofing
Pitch decides which materials you can use and what the job costs. Most shingle makers require at least 2/12, with extra underlayment below 4/12.
- Under 2/12: low slope, needs membrane roofing
- 2/12 to 4/12: shingles with double underlayment
- 4/12 to 9/12: standard, walkable for most crews
- Over 9/12: steep, priced higher for safety gear and time
Frequently asked questions
How do I calculate roof pitch?
Measure the rise in inches over a 12-inch level run. If the roof rises 6 inches in 12, the pitch is 6/12.
What is a 6/12 roof pitch in degrees?
26.57 degrees. A 4/12 pitch is 18.43° and a 12/12 pitch is 45°.
What is the most common roof pitch?
Between 4/12 and 9/12 for houses. 6/12 is one of the most common.
What is a roof pitch multiplier?
The number you multiply a flat footprint by to get the sloped roof area. It's √(1 + (pitch ÷ 12)²).
Can I measure pitch from the ground?
Pitch-finder apps and aerial measurement reports can estimate it, but a level and tape on the roof or in the attic is the most accurate.