How to use this estimate
Measure vertical rise and horizontal run over the same section. Run is not the sloped length and, for a symmetrical gable, is typically half the horizontal span between the supporting walls. Both measurements use the same unit system. A flat surface has zero rise and is allowed.
The calculation
A worked example
A 6 ft rise over a 12 ft horizontal run gives 6:12 pitch, a 26.565° angle, 50% slope and a geometric rafter length of 13.416 ft.
Rafter length is triangle geometry only. It excludes overhangs, ridge deductions and joinery, and does not determine lumber size, structural capacity or permissible roof covering.
Common questions
Does a 6:12 pitch mean 6 degrees?
No. It means 6 units of vertical rise for 12 units of horizontal run, giving an angle of about 26.565 degrees.
References & method
Omni roof pitch reference. See how we check calculations. Reference links provide context; no supplier endorses this site.