Roof Pitch Calculator
Roof pitch (x/12), angle in degrees, slope percentage and rafter length from rise and run.
Inputs
m
Any unit — rise and run must use the same unit.
m
Results
- Pitch
- 4.5 / 12
- Angle
- 20.56 °
- Slope
- 37.5 %
- Rafter length (no overhang)
- 4.272 m
Formula
Pitch = rise ÷ run × 12
Angle = atan(rise ÷ run)
Rafter = √(rise² + run²)
Assumptions & limits
- Run is the horizontal distance from wall plate to ridge (half the span for a gable).
- Add eave overhang to the rafter length separately.
Worked example
1.5 ÷ 4 × 12 = 4.5/12; atan(0.375) = 20.56°; rafter = √(2.25 + 16) = 4.272 m.