Roof Pitch Calculator
Find your roof pitch in degrees and as a ratio from the rise and run.
Roof pitch
26.6°
- Ratio
- 6:12
- Slope
- 50 %
- Rafter length
- 4.47 m
Run is the horizontal distance from the wall to the ridge, not the full building width.
v1.0 · Reviewed September 2026
How this is worked out
The pitch angle is the arctangent of rise ÷ run. The ratio expresses the same slope as rise per 12 units of run, the percentage is rise ÷ run × 100, and the rafter length is the hypotenuse √(rise² + run²).
Worked example
- Rise 2 m
- Run 4 m
arctan(2 ÷ 4) = 26.6°, ratio 6:12, slope 50%, rafter √(2² + 4²) = 4.47 m
26.6°
Assumptions and limits
- Run is measured horizontally from the wall to the ridge, not across the whole building.
- The rafter length is geometric and excludes overhang and birdsmouth cuts.