How to Calculate Roof Pitch
Roof pitch is the roof rise divided by the horizontal run, usually shown as inches of rise over 12 inches of run. A 6/12 pitch means the roof rises 6 inches for every 12 inches across.
Roof Pitch Formula
Pitch over 12
Pitch = rise / run x 12
Angle
Degrees = arctan(rise / run)
Percent slope
Percent = rise / run x 100
Roof Pitch Chart
| Pitch | Angle | Percent Slope | Typical Meaning |
|---|---|---|---|
| 2/12 | 9.46 deg | 16.7% | Low slope |
| 3/12 | 14.04 deg | 25% | Low slope |
| 4/12 | 18.43 deg | 33.3% | Common residential |
| 5/12 | 22.62 deg | 41.7% | Common residential |
| 6/12 | 26.57 deg | 50% | Common residential |
| 8/12 | 33.69 deg | 66.7% | Steep |
| 10/12 | 39.81 deg | 83.3% | Steep |
| 12/12 | 45 deg | 100% | Very steep |
How to Measure Roof Pitch Safely
- Use an attic rafter, fascia, or safe accessible edge when possible instead of climbing on a roof.
- Hold a level horizontally and mark a 12-inch run.
- Measure the vertical distance from the roof surface or rafter to the level at the 12-inch mark.
- Enter that rise and 12-inch run into the calculator.
Roof Pitch and Material Planning
Roof pitch affects drainage speed, material choice, flashing details, ventilation, labor difficulty, and safety planning. Low-slope roofs often need different waterproofing details than conventional pitched roofs, while steep roofs may need extra access and fall-protection planning.