Roof pitch multiplier & angle chart
The pitch multiplier turns a flat footprint into true roof area: M = √(1 + (rise/12)²). Multiply your footprint by M to get roof surface area, then divide by 100 for roofing squares. Use the roof area calculator for your own numbers.
| Pitch | Angle | Grade | Multiplier |
|---|---|---|---|
| 1/12 | 4.8° | 8% | 1.0035 |
| 2/12 | 9.5° | 17% | 1.0138 |
| 3/12 | 14.0° | 25% | 1.0308 |
| 4/12 | 18.4° | 33% | 1.0541 |
| 5/12 | 22.6° | 42% | 1.0833 |
| 6/12 | 26.6° | 50% | 1.1180 |
| 7/12 | 30.3° | 58% | 1.1577 |
| 8/12 | 33.7° | 67% | 1.2019 |
| 9/12 | 36.9° | 75% | 1.2500 |
| 10/12 | 39.8° | 83% | 1.3017 |
| 12/12 | 45.0° | 100% | 1.4142 |
| 14/12 | 49.4° | 117% | 1.5366 |
| 16/12 | 53.1° | 133% | 1.6667 |
| 18/12 | 56.3° | 150% | 1.8028 |
| 24/12 | 63.4° | 200% | 2.2361 |
Roof area = flat footprint × multiplier; roofing squares = roof area ÷ 100.