6.5/12 roof pitch in degrees
A 6.5/12 roof pitch is 28.4429°. That is a 54.17% grade, a slope ratio of 1 : 1.8462, and a rafter factor of 1.137279, and the angle is irrational so it carries the ≈.
Change the pitch
28.4429°≈
Multiply your run by 1.137279 for the rafter length. The cuts and the birdsmouth are in the app.
Rafter length at 6.5/12, by span
Run is half the span on a symmetrical gable. Length is along the rafter, before any birdsmouth, ridge or tail is taken off.
| Building span | Run | Rafter length | Decimal feet |
|---|---|---|---|
| 20 ft | 10 ft | 11' 4-1/2" | 11.373 ft |
| 24 ft | 12 ft | 13' 7-3/4" | 13.647 ft |
| 28 ft | 14 ft | 15' 11-1/16" | 15.922 ft |
| 32 ft | 16 ft | 18' 2-3/8" | 18.196 ft |
| 36 ft | 18 ft | 20' 5-5/8" | 20.471 ft |
Every row is the run multiplied by 1.137279, the rafter factor for 6.5/12. The same figure for every pitch is on the full roof pitch chart.
What 6.5/12 means on the roof
Six and a half in twelve is the half twelfth that changes the labour bill. Six is about the limit of what a roofer will walk freely and this is past it, so the same roof area costs more to cover than one framed half an inch shallower, for reasons that have nothing to do with how much of it there is.
The working is the arctangent of the rise over the run: atan(6.5 ÷ 12) = 28.4429°. The rafter factor is the hypotenuse of the same triangle over its base, √(12² + 6.5²) ÷ 12, which is why multiplying any run by 1.137279 gives the rafter. That figure is the roof pitch multiplier, and it is the same number whatever the size of the roof.
Shingle slope limits quoted here are from the IRC, the United States model code. Your state, province or county may amend them, and several do.
