FRAMING
Rafter Length Estimator
Estimate rafter length from your roof dimensions. Enter the building run and roof pitch. Add an overhang to include the tail length. The calculator uses the pitch and run to calculate the sloped rafter length. Use the result to plan framing material.
How to Calculate Rafter Length Estimator
The calculator derives rise from the roof pitch, finds the sloped length with the Pythagorean theorem, and adds overhang after converting inches to feet.
- Rise = horizontal run x pitch / 12.
- Rafter length = square root(run squared + rise squared) + overhang in feet.
Frequently Asked Questions
What does a 6/12 roof pitch mean in this calculation?
It means the roof rises 6 inches for every 12 inches of horizontal run. Enter 6 in the pitch field for a 6/12 pitch.
Does the result include birdsmouth cuts or ridge details?
No. It is a geometric length estimate plus the entered overhang. Allow for plumb cuts, birdsmouths, ridge-board details, and field measurements when cutting rafters.