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Convert roof pitch rise and run to angle, percent slope, and pitch factor. Essential for roofing material estimates, rafter layout, and drainage design.
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Half the clear span from wall plate to ridge, minus half the ridge board thickness (typically 3/4″ to 1-1/2″).
Run = (Span − Ridge Board) ÷ 2Vertical height from plate to ridge for the given pitch. A 6/12 pitch on 12 ft run gives 6 ft rise.
Rise = Run × (Pitch Rise ÷ 12)Hypotenuse of the right triangle plus overhang measured along the slope. Add tail length for eave projection.
Length = √(Run² + Rise²) + Overhang ExtensionUpdated: July 2026
Run = 11.92 ft, rise = 3.97 ft, rafter body ≈ 12.56 ft plus overhang tail ≈ 1.06 ft for 12″ eave.
Smaller span with steeper pitch: run 8 ft, rise 4 ft, rafter length ≈ 8.94 ft before overhang. Use for cutting list on 10 ft or 12 ft lumber.
Ridge beam designs may use full run without ridge board subtraction — adjust span input per engineered plan.
Determine common rafter length for stick-framed roofs before cutting lumber. Enter building span, pitch, and overhang to get rafter run, rise, and true diagonal length including tail for fascia overhang.