CALCULATION METHOD
How many bundles of shingles do I need?
Find the total sloped roof area, add an allowance for cuts and waste, divide by 100 to get roofing squares, then multiply by the bundle coverage for your exact shingle product. Round bundles up to whole packages.
Pitch factor = √(1 + (rise ÷ run)²)
Roof area = footprint including overhang × pitch factor
Order area = roof area × (1 + waste allowance)
Roofing squares = order area ÷ 100 sq ft
Bundles = roofing squares × bundles per square, rounded up
40 × 25 ft roof example
A 40 × 25 ft building with a 1 ft overhang on every side has a 42 × 27 ft roof footprint. At a 6:12 pitch, the 1.1180 pitch factor produces about 1,267.9 sq ft of roof area. With 10% waste, order for 1,394.6 sq ft, or 13.95 squares. At three bundles per square, that is 42 bundles.
Roofing squares and bundle chart
A roofing “square” is 100 sq ft. The quick chart assumes three bundles per square and does not include waste.
| Roof area | Roofing squares | Bundles at 3/square |
|---|---|---|
| 1,000 sq ft | 10 | 30 |
| 1,500 sq ft | 15 | 45 |
| 2,000 sq ft | 20 | 60 |
| 2,500 sq ft | 25 | 75 |
| 3,000 sq ft | 30 | 90 |
Why bundles per square can vary
Three bundles per square is common for many asphalt shingles, but it is not universal. Heavier or specialty shingles may be packaged as four or five bundles per square. Use the coverage printed on the wrapper or current product data rather than assuming every bundle covers one-third of a square.
How much waste should I add?
The calculator starts at 10%. A simple gable may have less cutting than a hip roof with valleys, dormers, and many penetrations. Complex layouts can require a different allowance, so adjust the setting after reviewing the roof plan and installer’s takeoff.
Ridge caps, starter strips, and field shingles
Field-shingle bundles do not automatically account for dedicated starter-strip or hip-and-ridge products. Their lineal coverage varies, so the optional ridge-cap input uses the exact coverage per bundle you enter. Estimate starter strips separately from total eave and rake length.
GAF bundle and roofing-square guide for the 100 sq ft square, common three-bundle packaging, and 10–15% planning allowance; IKO bundle coverage guide for product-dependent coverage, including three- to five-bundle examples. Accessed September 11, 2026.