How to use the roofing calculator
- Measure the outside length and width of the house, or of each section for L-shaped houses, and run each section separately.
- Add the eave overhang. It is often 1 to 2 ft on each side and is part of the roof you shingle.
- Pick your pitch. If you do not know it, measure the rise over a 12 in level held against a rafter in the attic.
- Use the bundles on your shingle wrapper if it differs from 3 per square.
The formula
Flat area = (length + 2 × overhang) × (width + 2 × overhang). Roof area = flat area × pitch factor, where the pitch factor is √(1 + (rise ÷ 12)²). Squares = roof area × (1 + waste%) ÷ 100, and bundles = squares × 3, rounded up.
Worked example: a 50 × 30 ft house, 1 ft overhang, 6/12 pitch
Flat area (52 × 32) = 1,664 sq ft. × 1.118 = 1,860 sq ft of roof. With 10% waste: 2,046 sq ft = 20.5 squares, so buy 62 bundles.
Pitch factors
| Pitch | Multiply flat area by |
|---|---|
| 2/12 | 1.014 |
| 3/12 | 1.031 |
| 4/12 | 1.054 |
| 5/12 | 1.083 |
| 6/12 | 1.118 |
| 7/12 | 1.158 |
| 8/12 | 1.202 |
| 9/12 | 1.250 |
| 10/12 | 1.302 |
| 12/12 | 1.414 |
Shingles for common footprints
6/12 pitch, no overhang, 10% waste.
| Footprint | Roof area | Squares | Bundles |
|---|---|---|---|
| 1,000 sq ft | 1,118 sq ft | 12.3 | 37 |
| 1,500 sq ft | 1,677 sq ft | 18.4 | 56 |
| 2,000 sq ft | 2,236 sq ft | 24.6 | 74 |
| 2,500 sq ft | 2,795 sq ft | 30.7 | 93 |
Before you order
- Hip and ridge caps, starter strips, underlayment, drip edge and nails are ordered separately. Your supplier can work them out from the squares.
- Roofing is dangerous work. For steep or high roofs, get quotes from licensed roofers and use this number to check them.