How it's calculated
pitch = (rise ÷ run) × 12, angle = arctan(rise ÷ run), slope% = (rise ÷ run) × 100
rise = vertical rise, run = horizontal run, pitch = inches of rise per 12 in of run (x:12). Rafter multiplier = √(1 + (rise÷run)²) gives true rafter length per unit of run.
Reference ranges
| Pitch (x:12) | Angle | Slope % |
|---|---|---|
| 3:12 | 14.0 deg | 25% |
| 4:12 | 18.4 deg | 33% |
| 6:12 | 26.6 deg | 50% |
| 9:12 | 36.9 deg | 75% |
| 12:12 | 45.0 deg | 100% |
Common questions
What does a 4:12 pitch mean?
The roof rises 4 inches for every 12 inches of horizontal run, which works out to about 18.4 degrees.
Which pitches suit asphalt shingles?
Asphalt shingles generally need at least a 2:12 pitch, with low-slope methods required below 4:12.