Roof Pitch & Rafter Length
Convert roof rise and run to pitch ratio, angle and slope percent, and find the rafter length for a span, free online.
About this calculator
Pitch is written as rise : 12 (inches of rise per 12 inches of run). Angle = arctan(rise ÷ run); slope % = rise ÷ run × 100. Rafter length = (span ÷ 2) ÷ cos(angle), plus any overhang. Steeper roofs have a larger roof area for the same footprint.