A roof pitch calculator converts between the ways a roof slope is described. Enter the rise and run or a roof angle, and the tool returns the pitch as an x-in-12 ratio, in degrees, and as a percentage slope — useful for ordering materials, checking a drawing, or matching an existing roof.
How it works
The slope is the rise ÷ run ratio. From rise and run the tool computes:
- x-in-12 ratio = rise ÷ run × 12 (vertical rise per 12 of horizontal run)
- Angle = arctan(rise ÷ run), in degrees
- Percentage slope = rise ÷ run × 100
In angle mode it works backward: the slope is tan(angle), so rise-in-12 = tan(angle) × 12 and percentage = tan(angle) × 100. All three formats describe the same roof slope.
Example
A roof with a rise of 4 over a run of 12 (a 4:12 roof):
- Ratio = 4 in 12
- Angle = arctan(4 ÷ 12) ≈ 18.43°
- Percentage = 4 ÷ 12 × 100 ≈ 33.3%
| x-in-12 | Angle | % slope |
|---|---|---|
| 3:12 | 14.0° | 25% |
| 4:12 | 18.4° | 33.3% |
| 6:12 | 26.6° | 50% |
| 12:12 | 45.0° | 100% |
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