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Roof area is larger than floor area; multiply the footprint by a pitch factor or measure each plane.
Squares and bundles
Roofing is sold by the square: 100 sq ft of roof. Most architectural and 3-tab asphalt shingles come 3 bundles to a square. A 2,000 sq ft roof surface is 20 squares, or 60 bundles before waste.
Pitch changes the area
A sloped roof has more surface than its footprint. Multiply the footprint by the pitch factor: 4/12 = 1.054, 6/12 = 1.118, 8/12 = 1.202, 12/12 = 1.414. Add about 10% waste for a simple gable roof and 15% for hips and valleys.
Frequently asked questions
What is a roofing square?
100 square feet of roof.
How do I find my roof pitch?
Measure how many inches the roof rises over 12 inches of horizontal run.
Are starter strips and ridge caps included?
No; buy them separately based on the eaves and ridge length.