Rafter Calculator

How It Works

1. Enter span and pitch. Type the building span (ft) and roof pitch as rise per 12 inches (e.g. 6/12).
2. Get rafter length. The calculator finds run, rise, and body length using the Pythagorean theorem.
3. Add overhang. Enter building width, overhang, and ridge beam thickness for the full rafter cut length.
4. Birdsmouth cuts. See plumb cut angle, seat cut depth, and heel dimensions for your rafter depth.
5. Hip & valley factors. Use slope and hip factors to estimate diagonal rafter lengths.

Also see our Recessed Lighting Calculator or Construction Calculators.