How the roof pitch calculator works
Pitch is the rise in inches for every 12 inches of horizontal run, so a 6/12 roof rises 6 inches per foot. The calculator converts that to an angle, 26.6° for a 6/12 roof, and a slope percentage, 50%.
The pitch multiplier turns flat, plan-view area into true roof area. It is √(rise² + 144) ÷ 12, so a 6/12 roof has a multiplier of 1.118, and a 2,000 sq ft footprint at 6/12 is about 2,236 sq ft of roof. The hip and valley factor is a different number. Multiply a hip's or valley's common run, the level distance it covers from the wall line to the ridge, by it to get the hip or valley length when both planes share the pitch. At 12/12 it is 1.732, against an area multiplier of 1.414, so using it for area overstates the roof.
How to measure roof pitch
Hold a level against the roof deck, or against a rafter in the attic, and mark 12 inches along it. Measure plumb from that mark to the roof deck or rafter. That number is the rise. A phone angle app works too if you read it on the roof deck, a rafter, or the rake board, then enter the angle.
A measurement report's predominant pitch can hide steeper planes, so check each plane on a cut-up roof.
When is a roof steep?
It depends on who's asking. OSHA treats a roof steeper than 4/12 as steep for fall protection. The building code calls for two layers of underlayment from 2/12 to under 4/12 and doesn't allow asphalt shingles below 2/12. An approved self-adhered underlayment system may have different layer requirements. On an Xactimate estimate, steep charges are separate lines that start at 7/12, in bands such as 7/12 to 9/12 and 10/12 to 12/12, and they apply only to the planes in each band. Two-story roofs carry a separate high-roof charge.
FAQ
What is a 6/12 pitch in degrees?
About 26.6°, or a 50% slope.
What is a 4/12 pitch in degrees?
About 18.4°, or a 33% slope.
Do you add waste before or after the pitch multiplier?
After. Apply the multiplier to get the true roof area, then add waste for cutting. The roof square footage calculator does both.
Frontera's estimating software builds Xactimate-formatted estimates and supplements from your measurements and photos.