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How Many Bundles of Shingles Do I Need?
Quick answer: Asphalt shingles come 3 bundles to a square (100 sq ft), so a 20-square roof needs about 60 bundles plus 10% for waste.
Roofing is estimated in "squares," and the number that trips everyone up is the roof pitch. This guide shows how to turn your roof's footprint into squares, squares into bundles, and how to add the right underlayment and waste — then points you to the calculator that does it automatically.
Roofing is measured in squares
A roofing square equals 100 square feet of roof surface. It is the unit every supplier, contractor, and shingle wrapper uses. So the whole job is: find your total roof area, divide by 100, and you have your squares.
Why you can't just measure the footprint
The area of your roof is larger than the footprint of your house because the roof is sloped. To account for that, multiply your footprint area by the pitch multiplier for your roof.
| Roof pitch | Angle | Pitch multiplier |
|---|---|---|
| 4/12 | 18.4° | 1.054 |
| 6/12 | 26.6° | 1.118 |
| 8/12 | 33.7° | 1.202 |
| 10/12 | 39.8° | 1.302 |
| 12/12 | 45.0° | 1.414 |
Full chart in Roof Pitch to Angle. Example: a 6/12 roof over a 2,000 sq ft footprint has 2,000 × 1.118 = 2,236 sq ft of actual roof surface.
Bundles per square
Standard architectural and 3-tab asphalt shingles come 3 bundles to a square, with each bundle covering about 33.3 sq ft. So once you know your squares, multiply by 3:
Underlayment
Underlayment goes down before the shingles. Coverage depends on the weight:
| Underlayment | Coverage per roll | Squares per roll |
|---|---|---|
| #15 felt | ~400 sq ft | 4 squares |
| #30 felt | ~200 sq ft | 2 squares |
| Synthetic | ~1,000 sq ft | 10 squares |
See Roof Vent Calculator to confirm attic ventilation while you're speccing the roof.
Add a waste factor
Cuts at hips, valleys, and rakes create waste. Add:
- 10% for a simple gable roof with few penetrations.
- 15–20% for complex roofs with valleys, hips, dormers, or skylights.
Worked example
2,000 sq ft footprint, 6/12 pitch, simple gable:
- Roof area: 2,000 × 1.118 = 2,236 sq ft
- Squares: 2,236 ÷ 100 = 22.4 squares
- Bundles: 22.4 × 3 = 67 — add 10% → ~74 bundles
- #15 felt: 22.4 ÷ 4 = ~6 rolls
Which calculator should you use?
Let the tool apply the pitch multiplier, bundle math, and waste for you:
- Squares, bundles, and underlayment → Roof Shingle Calculator
- Convert rise/run into pitch, angle, and multiplier → Roof Pitch Calculator
- Estimate full replacement cost → Roof Cost Calculator
- Metal panels and screws → Metal Roof Calculator
Frequently asked questions
How many bundles of shingles are in a square?
Three bundles cover one square (100 sq ft); each bundle covers about 33.3 sq ft.
How do I calculate how many shingles I need?
Footprint area × pitch multiplier ÷ 100 = squares; squares × 3 = bundles. Add 10–15% waste.
How much waste should I add?
10% for a simple gable, 15–20% for roofs with valleys, hips, or dormers.