Roof Pitch, Slope & Rafter Angle Calculator
Calculate roof pitch rise over 12" run, rafter slope angle in degrees, pitch area multiplier factor, true rafter lengths with eave overhangs, and roofing squares.
Calculated Results
Frequently Asked Questions
What does roof pitch (e.g. 6/12) mean?
Roof pitch expresses vertical rise over 12 inches of horizontal run. A 6/12 pitch means the roof rises 6 vertical inches for every 12 horizontal inches (slope = 0.50, angle = 26.57°).
What is the pitch multiplier factor in roofing?
The pitch multiplier is the hypotenuse factor calculated as sqrt(1 + (Rise/12)^2). Multiplying flat ground square footage by this factor yields the true surface square footage of the pitched roof.
What is the minimum roof slope for asphalt shingles?
The International Residential Code (IRC) requires a minimum 2/12 pitch for asphalt shingles with double underlayment, and at least 4/12 for standard single underlayment. Roofs under 2/12 require flat roofing membranes (EPDM, TPO, Modified Bitumen).
What pitch is considered 'Walkable' without safety ropes?
Roofs with a 4/12 or 5/12 pitch are generally walkable by tradespeople. At 6/12 and above, foot traction decreases significantly and OSHA safety harnesses and roof jacks are standard.