Roofing estimates live and die on one number: bundles. Order too few and you pay a second delivery fee mid-job; order too many and you’re stuck with non-returnable stock. The good news is that shingle quantity follows simple, standard arithmetic once you know your roof’s footprint and pitch.
Start by getting the roof’s flat area and slope factor with our roof pitch and area guide, then come back to the quantities below.
The Base Rule
Almost all asphalt shingles in North America are sold in bundles covering 33.3 square feet — three bundles to a “square” (100 sq ft). So the core formula is:
Bundles = (roof area in sq ft ÷ 100) × 3
Add the Waste Factor
Cutting around hips, valleys, and ridges wastes material. Standard waste allowances:
| Roof complexity | Waste | Multiplier |
|---|---|---|
| Simple gable, few penetrations | 5% | 1.05 |
| Hips, a couple of valleys | 10% | 1.10 |
| Complex, many valleys/dormers | 15% | 1.15 |
A Worked Example
Take a house with a 1,800 sq ft footprint and a 6/12 pitch:
- Roof area ≈ 1,800 × 1.118 (slope factor for 6/12) = 2,012 sq ft
- Base squares = 2,012 ÷ 100 = 20.1
- Base bundles = 20.1 × 3 = 60.3
- With 10% waste = 60.3 × 1.10 = 66.4 → order 67 bundles
Don’t Forget the Accessories
Bundles aren’t the whole order. Per 100 sq ft of roof you also need:
- Underlayment: ~1 roll per 4 squares (synthetic)
- Ridge cap: ~1 bundle per 35 linear feet of ridge and hip
- Starter strip: ~1 bundle per 100 linear feet of eave
- Nails: ~320 nails per square (about 2 kg per square)
Pitch Changes Everything
A 4/12 roof has a slope factor near 1.054; a 9/12 roof is near 1.25. Measuring the footprint and multiplying gives you flat area — but applying the same item count to a steep roof understates both area and waste. Always convert to true roof area before dividing by 100.
FAQ
Can I return leftover bundles? Often yes, unopened, if the dye lot matches — but many suppliers charge a restocking fee. Ordering 5–10% over is usually cheaper than a return trip plus a second minimum-order fee.
How long does a job take? Two experienced roofers install roughly 20–25 squares per day on a straightforward gable, so a 20-square roof is a 1–2 day job.
One square = how many bundles? Three, for standard three-tab and most architectural shingles. Check the bundle coverage printed on the wrapper — a few premium lines cover slightly less.
Measure the footprint, multiply by the slope factor, divide by 100, multiply by 3, add waste. That’s the whole calculation.
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