Determine the pitch of a rafter

Find the pitch of any bastard pitch rafter with incredible ease and accuracy with the free Builder Fraction Calculator app.

Learn how to determine the roof pitch equivalent for any known rise and known run with the workshop below. This way you can use a framing square to get more precise cuts on rafters and other framing components.

Install now:

iOS download

Android download

Open app

Builder Fraction Calculator

Click on menu in the top left.

Select Diagonal

Menu for pitch calculator

Click on diagonal at the top.

The Rise


Enter the rise and click equals.

The Run


Enter the run and click equals.


Rafter pitch

The rafter pitch is 4 / 12.