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Roof pitch is the rise in inches for every 12 inches of horizontal run, written like 6/12. The angle is arctan(rise ÷ run) — a 6/12 roof is 26.6°.
With the building span, the rafter length (without overhang) is half the span × the pitch multiplier, and the ridge height is half the span × rise ÷ run.
| Rise | 6 |
| Run | 12 |
| Building span (optional, same unit) | 30 |
| Roof pitch | 6/12 |
| Angle | 26.57° |
| Slope | 50% |
| Pitch multiplier | 1.118 |
| Rafter length (no overhang) | 16.771 (same unit as span) |
| Ridge height above wall | 7.5 |
6/12 = 26.57°.
| Rise | 1.2 |
| Run | 3 |
| Building span (optional, same unit) | 6 |
| Roof pitch | 4.8/12 |
| Angle | 21.8° |
| Slope | 40% |
| Pitch multiplier | 1.077 |
| Rafter length (no overhang) | 3.231 (same unit as span) |
| Ridge height above wall | 1.2 |
4.8/12, 21.8°.
18.4°.
Between 4/12 and 9/12 for houses; 6/12 (26.6°) is very common.
2/12 with special underlayment; 4/12 for standard installation.
Hold a level horizontally 12 inches from the roof and measure the vertical distance up to the roof surface.