Roof Pitch Calculator
Convert rise and run into roof pitch, angle in degrees, and the slope-length multiplier.
Roof pitch describes steepness as inches of rise per 12 inches of horizontal run — a "6/12" roof rises 6 inches for every foot it runs horizontally. That single ratio drives several other numbers a crew needs: the angle in degrees for setting a saw or speed square, and the slope-length multiplier, which tells you how much longer the actual rafter is compared to the flat horizontal distance it spans — essential for ordering rafters, trusses, or roofing material to the right length.
Frequently Asked Questions
What roof pitch is considered steep?
Pitches under 4/12 are considered low-slope, 4/12 to 9/12 are standard residential pitches, and anything above 9/12 (about 37 degrees) is generally considered steep and may need special safety equipment to work on.
How do I find the actual rafter length from the pitch?
Multiply the horizontal run by the slope-length multiplier this calculator gives you. For example, a 6/12 pitch has a multiplier of about 1.118, so a 20 ft run needs a rafter of about 22.4 ft before overhang.
Guidence
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Convert rise and run into roof pitch, angle in degrees, and the slope-length multiplier.