How to calculate roofing
Shingles are estimated from the sloped roof area, not the ground footprint:
Roof area = footprint × pitch factor, then squares = area ÷ 100, and bundles = squares × 3
The pitch factor converts your flat footprint into the actual sloped surface. Add a waste allowance and round up — running short partway up a roof is not an option.
Pitch factors
| Roof pitch | Multiply footprint by |
|---|---|
| Flat to 3:12 | ~1.03 |
| 4:12 | ~1.06 |
| 6:12 | ~1.12 |
| 8:12 | ~1.20 |
| 12:12 | ~1.41 |
Good to know
- A "square" = 100 sq ft. Roofers measure and quote in squares.
- 3 bundles per square is standard for architectural shingles — check the wrapper.
- Complex roofs waste more. Hips, valleys, and dormers mean more cuts — lean toward 15% waste.
- This is a material estimate. For steep or complex roofs, hiring a pro is strongly recommended.