10/12 roof pitch: 39.81 degrees
A 10/12 roof pitch is 39.8056° to four places. Its multiplier, or rafter factor, is 1.301708, its grade is 83.33% and its slope ratio is 1 : 1.2.
Change the pitch
39.8056°≈
Multiply your run by 1.301708 for the rafter length. Hips and valleys at this pitch are in the app.
Rafter length at 10/12, 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 | 13' 3/16" | 13.017 ft |
| 24 ft | 12 ft | 15' 7-7/16" | 15.620 ft |
| 28 ft | 14 ft | 18' 2-11/16" | 18.224 ft |
| 32 ft | 16 ft | 20' 9-15/16" | 20.827 ft |
| 36 ft | 18 ft | 23' 5-3/16" | 23.431 ft |
Every row is the run multiplied by 1.301708, the rafter factor for 10/12. The multiplier for every pitch is on the roof pitch multiplier table.
What 10/12 means on the roof
Ten in twelve is steep. It sheds snow and water readily, it is not walkable, and everything above the plate line needs staging.
The working is the arctangent of the rise over the run: atan(10 ÷ 12) = 39.8056°. The rafter factor is the hypotenuse of the same triangle over its base, √(12² + 10²) ÷ 12, which is why multiplying any run by 1.301708 gives the rafter. That figure is the roof pitch multiplier, and it is the same number whatever the size of the roof.
A hip or valley where both roofs are 10/12 runs at 45° across the plan, so it is longer than the common rafter beside it: 1.6415 ft of hip for every foot of common run, which is 16' 5" over a 10 ft common run against 13' 3/16" for the rafter.
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.
Other pitches: 1/12 · 2/12 · 3/12 · 4/12 · 4.5/12 · 5/12 · 6/12 · 6.5/12 · 7/12 · 8/12 · 9/12 · 11/12 · 12/12. Every pitch from 1/12 to 24/12 is on the roof pitch to degrees chart.
