A square is an area unitOne roofing square equals 100 square feet. Bundle coverage varies, so use the bundle count printed for the selected shingle system.
From footprint to sloped roof area
For a simple gable roof, the building footprint area can be multiplied by a pitch factor to approximate both sloped roof planes. The calculator then applies the selected allowance before dividing by 100 square feet per roofing square.
Enter overall roof-plan dimensions, including the horizontal projection of overhangs. Complex roofs should be divided into measurable planes instead of treated as one rectangle.
- 3:12 pitch factor: about 1.031.
- 6:12 pitch factor: about 1.118.
- 12:12 pitch factor: about 1.414.
Bundles depend on the product
Many laminated shingles are packaged near three bundles per square, but that is not universal. Starter, ridge-cap, hip-and-ridge, underlayment, flashing, membrane, vents, nails, and sealants are separate quantities with their own coverage.
Waste follows roof complexity
Straight gable roofs normally create less cutting than roofs with several valleys, dormers, hips, transitions, or short planes. Replace the starting allowance with a value based on the actual geometry and the manufacturer’s instructions, and confirm the order with a roofing supplier or qualified contractor.
BuildMath Lab provides planning estimates, not engineering, code approval, or a supplier quote. Confirm the final order with the product manufacturer, supplier, plans, and qualified professional.