How to calculate roofing shingles
Roofing is measured in "squares," where one square equals 100 square feet of roof. The catch is pitch: a sloped roof has more surface than the flat footprint below it, so the ground dimensions are multiplied by a pitch factor to get true roof area.
roof area = length × width × pitch factor
squares = (roof area × 1.10) ÷ 100
bundles = squares × 3
Worked example
A 40 ft × 30 ft building with a 6/12 pitch has 1,200 sq ft of footprint × 1.12 = 1,344 sq ft of roof. Add 10% waste for about 1,478 sq ft, or 14.8 squares. At 3 bundles per square, that's about 45 bundles.
How many bundles of shingles per square?
Most architectural asphalt shingles come 3 bundles to the square. Here's how the key materials scale:
| Material | Coverage | Notes |
|---|
| Shingle bundles | 3 bundles per square | ~33 sq ft each |
| Underlayment | ~4 squares per roll | Synthetic, 10 sq roll |
| Roofing nails | ~2.5 lb per square | 4 nails per shingle |
Frequently asked questions
How many bundles of shingles do I need for a 1,500 sq ft roof?
A 1,500 square foot roof is 15 squares, needing about 45 bundles at 3 bundles per square, plus a bit more for waste, starter, and ridge caps.
What is a roofing square?
A roofing square equals 100 square feet of roof surface. Roofers price and order materials by the square rather than by the individual shingle.
Why does roof pitch matter?
A steeper roof has more surface area than the flat footprint beneath it. Multiplying by a pitch factor converts your ground measurements into the true roof area.
How much extra should I add for waste?
Add about 10% for standard roofs to cover cuts, starter strips, and ridge caps. Complex roofs with many valleys and hips may need 15% or more.