A unit of roof measurement equal to 100 square feet — the standard way roofers measure, quote, and order materials.
Roofers measure in squares because shingle bundles, underlayment, and labor pricing all scale in squares. A 30-square roof has 3,000 square feet of roof surface — though pitch increases the actual area beyond the building footprint.
When ordering, expect 3 bundles of architectural shingles per square, plus 10-18% waste depending on roof complexity.