construction calculator
Roof Pitch & Rafter Length Calculator
Find rafter length, slope factor, and roof angle from the pitch (rise per 12) and building span.
How it works
Slope factor = sqrt(rise^2 + 12^2) / 12. Rafter = (span / 2 + overhang) x slope factor.
Worked example
A 6/12 pitch on a 24 ft span: slope factor 1.118, rafter = 12 x 1.118 = 13.42 ft (26.6 degrees).
When to use it
- Rise per 12 is the X in an X/12 pitch.
- This is line length; subtract half the ridge thickness and adjust for the plumb cut.