What angle is a 4/12 pitch?
Answer
A 4/12 roof pitch has an angle of 18.43 degrees above horizontal.
A measurement from a plumb line gives a complementary seat-cut angle of 71.57 degrees.
| Value | Result |
|---|---|
| Rise for a 12-unit run | 4 units |
| Roof angle | 18.43 degrees |
| Slope | 33.33% |
| Rafter multiplier | 1.0541 |
| Line length for a 12 ft run | 12.649 ft |
Angle formula
Divide 4 by 12. Calculate the inverse tangent of 0.3333.
The result is 18.4349 degrees. The value is 18.43 degrees to two decimal places.
Rafter length at 4/12
Multiply the horizontal run by 1.0541. The result is the rafter line length before the overhang.
Use the rafter calculator for the ridge correction, tail length, and stock length.
Cut angles
The plumb-cut angle equals 18.43 degrees from square. The seat-cut angle is the complementary 71.57-degree angle.
Important information
- Confirm the angle reference on the saw or square.
- Make a test mark before the first rafter cut.