Estimates — add extra for waste and confirm with your supplier.
Roof area is the footprint times a pitch multiplier (steeper roofs have more surface). A 'square' is 100 sq ft, and most shingles come 3 bundles per square. We add waste for cuts and ridges.
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100 square feet of roof surface.
Steeper roofs have more surface than their flat footprint.
Usually 3 per square; check your shingle brand.
No — measure on-site; this excludes complex features.