Roof Pitch Calculator
Convert roof pitch between every form it gets quoted in: rise over run (like 6/12), angle in degrees, percentage slope, and the slope factor you multiply footprint area by to get true roof area.
Enter any one of them and the calculator returns the rest, along with rafter length for a given span.
How to use the roof pitch calculator
Enter a pitch as rise/run, degrees or percent.
Read the other three forms instantly.
Use the slope factor for your area calculation.
Why use the Build Tally roof pitch calculator
Four-way conversion
Rise/run, degrees, percent and slope factor.
Rafter length
Calculates rafter run for a given span.
Feeds the area tools
The slope factor plugs straight into roof area.
No sign-up
Runs entirely in your browser.
The four ways pitch gets expressed
Roofers quote pitch as rise over run — 6/12 means six inches of rise per twelve inches of horizontal run. Architects and engineers often use degrees, and 6/12 is 26.57°. Some specifications use percentage slope, where 6/12 is 50%. Estimators use the slope factor, the multiplier that converts footprint area into roof area, which for 6/12 is 1.118. All four describe the same roof, and this calculator moves between them so nothing gets lost translating a spec.
Measuring pitch on an existing roof
The safest method is from inside the attic: hold a level horizontally against a rafter, mark 12 inches along it, and measure the vertical distance from that mark up to the rafter's underside — that measurement is your rise. From outside, you can hold a level against a gable end at ground level and do the same. Avoid measuring on the roof surface itself; the difference between a 5/12 and a 6/12 is not worth a fall.
What pitch means for materials
Pitch determines what you can put on a roof. Asphalt shingles are generally rated down to 4/12 with standard installation, and 2/12 to 4/12 requires a doubled underlayment and specific manufacturer detailing. Below 2/12 you need a membrane rather than shingles. At the other end, steep roofs over about 8/12 need extra fasteners, are considerably harder to work on, and cost more to install for the same area. Check the manufacturer's instructions for your specific product.
Read the guide: Roof Pitch Explained: Rise Over Run, Degrees and the Slope Factor
Frequently asked questions
What is roof pitch?
The vertical rise in inches over 12 inches of horizontal run. A 6/12 roof rises six inches for every foot of run.
What is a 6/12 pitch in degrees?
26.57 degrees, which is a 50% slope and a slope factor of 1.118.
How do I convert roof pitch to angle?
The angle is the arctangent of rise divided by run. Enter either form above and the calculator converts it.
What is a slope factor?
The multiplier that converts footprint area to actual roof area. Multiply your footprint by it to get the surface a roofer will cover.
How do I measure my roof pitch?
From inside the attic: hold a level against a rafter, mark 12 inches, and measure vertically from that mark to the rafter. That is your rise.
What is the minimum pitch for shingles?
Generally 4/12 with standard installation, and 2/12 with doubled underlayment. Below that, use a membrane roof. Follow the manufacturer's instructions.
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