Roof pitch to angle for timber truss brackets
Chart, formula, and how to measure your truss.
Truss plates are cut to the angle of your rafters, so the pitch has to be right before we cut. Roof pitch is rise over a 12" run: an 8/12 roof rises 8" for every 12" across.
Pitch to angle chart
| Pitch | Rafter angle from level | Angle at the peak |
|---|---|---|
| 6/12 | 26.6° | 126.9° |
| 8/12 | 33.7° | 112.6° |
| 10/12 | 39.8° | 100.4° |
| 12/12 | 45.0° | 90.0° |
Our standard sets come in these four pitches: 6/12, 8/12, 10/12, 12/12. Anything else (7/12, 9/12, 14/12, or a measured angle like 31°) is a custom quote, and we send a drawing before we cut.
The formula
Angle = arctan(rise ÷ 12). For 8/12, arctan(8 ÷ 12) = 33.7°. The angle at the peak between two rafters is 180° minus twice the rafter angle.
How to measure an existing truss
- Hold a level against the underside of a rafter, with one end touching the rafter.
- Measure 12" along the level from that point.
- Measure straight up from the 12" mark to the rafter. That number is your rise: 8" means 8/12.
- Or set a digital angle finder or phone level app on the top edge of the rafter and read the degrees.
Not sure? Send a photo with a level in it on the quote form and we'll work it out with you.
Which sets use pitch?
King-post with diagonals, king-post truss plates and the fan / gable plate are all cut to pitch. Knee braces are 45° and don't depend on roof pitch.