Roofing quantities are quoted in squares, and the unit is exactly what it sounds like: one square is 100 square feet of roof surface. Shingle packaging is built around it — architectural shingles like GAF Timberline HDZ run 3 bundles per square at 33.33 sq ft per bundle, 64 pieces to the square — so an estimate expressed in squares converts directly to the bundles on the pallet. Ridge caps and underlayment follow their own coverages (a 1,000 sq ft synthetic roll is a 10-square roll), but the square remains the common denominator of the order.
Getting to squares from a house means converting footprint to sloped surface first: sloped area = horizontal footprint × √(1 + (rise/12)²), the standard pitch-factor method. A 50 × 30 ft footprint is 1,500 sq ft on plan; at a 6/12 pitch the factor is 1.118, giving 1,677 sq ft of actual roof — 16.77 squares before waste. Waste is applied on top (10% for simple roofs, 15% for complex ones), so the same roof orders as 18.4 squares, and every purchase then rounds up to whole units: 56 bundles, 2 rolls, whole boxes of nails.