Roofing is priced and ordered in "squares" — not square feet, not bundles. If you've never worked with a roofer or supplier before, that unit alone can make ordering confusing. Here's the full breakdown, from your home's footprint to the final bundle count.
Step 1: Find Your Roof's Footprint
Your roof's footprint is simply your home's length × width from a bird's-eye view — not the sloped surface. Measure the overall rectangle (or add up sections for an L-shaped or complex roof).
Step 2: Apply the Pitch Multiplier
A sloped roof has more actual surface area than its flat footprint. The steeper the pitch, the bigger the difference. Roof pitch is expressed as rise over a 12-inch run — a "6:12" pitch rises 6 inches for every 12 inches of horizontal run.
| Pitch | Multiplier | Extra Area |
|---|---|---|
| 3:12 (low slope) | 1.031 | +3% |
| 5:12 | 1.083 | +8% |
| 6:12 (common) | 1.118 | +12% |
| 8:12 | 1.202 | +20% |
| 10:12 | 1.302 | +30% |
| 12:12 (steep) | 1.414 | +41% |
Roof surface area = Footprint × Pitch Multiplier
Step 3: Convert to Roofing Squares
One roofing square equals 100 sq ft of roof surface. Divide your roof surface area by 100 to get the square count — this is the number roofers and suppliers actually use to quote and order materials.
Step 4: Bundles Per Square by Shingle Type
| Shingle Type | Bundles per Square |
|---|---|
| 3-Tab Asphalt | 3 |
| Architectural / Dimensional Asphalt | 3 |
| Wood Shake | 4 |
Architectural shingles are heavier per bundle than 3-tab, but both are conventionally sold and counted 3 bundles to a square.
Worked Example
A 2,000 sq ft footprint at a 6:12 pitch: 2,000 × 1.118 = 2,236 sq ft of actual roof surface, or 22.36 squares. Add 10% waste for a simple gable roof: 24.6 squares. At 3 bundles per square for architectural shingles, that's 74 bundles.
Don't Forget Underlayment
One roll of standard synthetic underlayment covers about 4 squares (400 sq ft). For the example above, that's 7 rolls. Also budget for ridge cap shingles (sold separately, typically covering 20–35 linear feet per bundle) and starter strip along the eaves.
Frequently Asked Questions
How many bundles of shingles do I need per square? Most standard 3-tab and architectural asphalt shingles come 3 bundles per square (100 sq ft). Wood shake typically needs 4 bundles per square.
How does roof pitch affect the shingle count? A steeper pitch means more actual surface area than the footprint suggests — a 6:12 pitch adds about 12% more area, a 12:12 pitch adds about 41%.
What is a roofing square? A roofing square equals 100 square feet of roof surface — the standard unit roofers and suppliers use to price and order materials.
How much waste should I add for a roofing job? Add 10% for a simple gable roof, and 15% for roofs with hips, valleys, or dormers.