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Three bundles of standard 3-tab or architectural shingles cover one roofing square (100 sq ft). Some heavyweight designer shingles come 4-5 bundles per square, so check the wrapper before ordering.

From inside the attic, hold a level horizontally against a rafter, measure 12 inches out, then measure straight down to the rafter. That vertical measurement is your pitch: 6 inches down means a 6/12 pitch. You can also estimate it visually: most homes are 4/12 to 8/12.

A typical 2,000 sq ft single-story home has a roof of roughly 22-26 squares once pitch and overhangs are factored in. Two-story homes of the same size have smaller footprints, so their roofs are usually 13-17 squares.

Add 10% for a simple gable roof and 15% for roofs with hips, valleys, dormers, or skylights. Complex roofs generate more cut waste, and you want leftover shingles from the same lot for future repairs.