Convert roof rise and run into percent slope, a 1:n ratio, and the pitch angle.
| Slope (%) | – |
| Ratio | – |
| Angle (°) | – |
Use this calculator when you have a rise and a run from a rafter, a drawing, or a spirit level and want the pitch in three common forms.
Percent slope = (rise ÷ run) × 100. Ratio is written 1 : (run ÷ rise). Angle = arctan(rise ÷ run) in degrees. Rise and run can be entered in metres (m) or feet (ft); only the ratio of the two matters, so any consistent pair of lengths works. A 6-in-12 roof is the same as 6 m rise on 12 m run.
This is a right-triangle conversion. It does not size rafters, count shingles, or apply a building-code snow factor.
Rise: Vertical rise of the roof, in m or ft.
Run: Horizontal run for that rise, in m or ft. On a gable, this is often half the building width.
Slope (%): Pitch as a percent.
Ratio: Pitch as 1 : n, where n is run per unit of rise.
Angle: Pitch angle in degrees from the horizontal.
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