How many bundles of shingles do I need?
A roofing square is 100 sq ft of roof, and most 3-tab and architectural shingles come 3 bundles to a square. A 40 × 30 ft footprint with a 6/12 pitch has 1,342 sq ft of roof; with 10% waste that is 14.76 squares, or 45 bundles.
Worked example: a 40 × 30 ft roof at 6/12
- Footprint including overhangs: 40 × 30 = 1,200 sq ft.
- Pitch factor for 6/12: √(1 + (6 ÷ 12)²) = 1.118.
- Roof area: 1,200 × 1.118 = 1,342 sq ft.
- Squares with 10% waste: 1,342 ÷ 100 × 1.10 = 14.76 squares.
- Bundles: 14.76 × 3 = 44.3, rounded up to 45 bundles.
Roof pitch factors
Multiply the flat footprint by the pitch factor to get the sloped roof area. The last column shows the roof area over a 1,000 sq ft footprint.
| Pitch | Pitch factor | Roof area |
|---|---|---|
| 3/12 | 1.031 | 1,031 sq ft |
| 4/12 | 1.054 | 1,054 sq ft |
| 5/12 | 1.083 | 1,083 sq ft |
| 6/12 | 1.118 | 1,118 sq ft |
| 7/12 | 1.158 | 1,158 sq ft |
| 8/12 | 1.202 | 1,202 sq ft |
| 9/12 | 1.250 | 1,250 sq ft |
| 10/12 | 1.302 | 1,302 sq ft |
| 12/12 | 1.414 | 1,414 sq ft |
How the calculator works
Pitch factor = √(1 + (rise ÷ 12)²)
Roof area = length × width × pitch factor
Squares = roof area ÷ 100 × (1 + waste %)
Bundles = squares × bundles per square, rounded up
Measure the footprint to the edge of the overhangs, not the walls. For a roof where every plane has the same pitch, a hip roof and a gable roof over the same footprint have the same surface area, so the same formula works for both.
GAF recommends adding 10% to 15% for trim and waste. Use the higher figure for roofs with hips, valleys and dormers. Ridge caps, starter strips, underlayment and flashing are ordered separately.
Frequently asked questions
What is a roofing square?
A roofing square is 100 square feet of roof area, a 10 × 10 ft section. A roof with 24 squares has about 2,400 square feet of surface.
How many bundles of shingles are in a square?
Most standard 3-tab and architectural asphalt shingles come 3 bundles to a square, according to GAF. Some heavier lines need 4 bundles per square, so check the shingle specification.
How much waste should I add for shingles?
GAF suggests adding 10% to 15% for trim allowance and waste. A simple gable roof is near 10%; roofs with hips, valleys and dormers need more.
Does the estimate include ridge caps and starter strips?
No. The bundle count covers the field shingles only. Ridge caps, starter strips, underlayment, drip edge and flashing are measured and ordered separately.