How this calculator works
It takes your roof’s footprint, multiplies by a pitch factor to get the true sloped area, converts to roofing “squares” (100 sq ft each), then to shingle bundles at 3 bundles per square plus 10% waste.
Worked example — a 40 ft × 30 ft footprint, 6/12 pitch:
1,200 × 1.12 = 1,344 sq ft → 13.4 squares → 45 bundles with waste.
1,200 × 1.12 = 1,344 sq ft → 13.4 squares → 45 bundles with waste.
Measure footprint, not slope
Enter the building’s footprint (length × width as seen from above). The pitch factor converts it to the larger sloped surface area for you.
Frequently asked questions
How many bundles of shingles in a square?
3 bundles cover one roofing square (100 sq ft) for standard architectural shingles.
How much extra for waste?
About 10% for a simple gable roof; 15% for roofs with many hips and valleys.