Roof pitch calculator

Convert a roof's rise and run into x:12 pitch, degrees, percent slope, and rafter length.

Pitch = rise per 12 units of run. Angle = atan(rise/run). Slope factor multiplies the horizontal run to get the true slope length — rafter for a span = span ÷ 2 × factor.

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How to use

  1. Enter the rise and the run in the same unit.
  2. Optionally enter the building span for rafter length.
  3. Read pitch, angle, slope factor, and rafter.

What it supports

Pitch = rise per 12 of run; angle = atan(rise/run); slope factor = hypot(rise,run)/run. Rafter = span ÷ 2 × factor — this ignores ridge thickness, overhangs, and birdsmouth cuts. Any consistent unit works (in, cm, m).

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