Roof Pitch Calculator
Convert rise and run into roof pitch, angle in degrees, slope percentage and rafter length.
Rafter length is the straight line from wall plate to ridge; add the overhang and allow for the ridge board thickness when cutting.
About this tool
Enter the vertical rise and the horizontal run of a roof (in any unit, as long as both use the same one) to get the pitch as x:12, the angle in degrees, the slope in percent and the rafter length from plate to ridge.
Frequently asked questions
Divide the rise by the run. Pitch is usually written as inches of rise per 12 inches of run: a roof that rises 6 over a 12 run is a 6:12 pitch, which is 26.6° or a 50% slope.
Take the arctangent of rise ÷ run. Common pitches: 4:12 ≈ 18.4°, 6:12 ≈ 26.6°, 8:12 ≈ 33.7°, 12:12 = 45°.
It depends on the product — asphalt shingles commonly need at least 2:12 to 4:12 and many concrete and clay tiles need around 15–22.5°. Always follow the manufacturer's minimum.
With Pythagoras: √(rise² + run²). Add the overhang beyond the wall and adjust for the ridge board before cutting.
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