Roofers quote everything in squares: a '20-square roof' is 2,000 square feet of surface. To find yours, multiply the building footprint by the pitch multiplier (a 6/12 roof multiplies by 1.118) and add both roof planes.
Order 10% extra for straight gable roofs and 15% for hips, valleys and dormers — ridge caps, starter strips and cut waste consume it. Heavier premium shingles can run 4 or 5 bundles per square, so check the wrapper.
Squares to bundles (3-bundle shingles)
| Roof size | Squares | Bundles |
|---|---|---|
| 1,000 ft² | 10 | 30 |
| 1,500 ft² | 15 | 45 |
| 2,000 ft² | 20 | 60 |
| 3,000 ft² | 30 | 90 |