Roofers price and order materials by the square — a unit equal to 100 square feet of roof surface. Knowing your square count is the first step to understanding a quote or buying the right number of shingle bundles.
Footprint is not roof area
The area your roof covers on the ground (its footprint) is always smaller than the actual sloped surface, because the roof rises as it spans. The steeper the pitch, the bigger the difference. A pitch multiplier converts footprint to true area: a 4/12 pitch multiplies by about 1.05, while a 12/12 pitch multiplies by 1.41.
From area to squares to bundles
Once you have the sloped area, divide by 100 to get squares. Standard architectural and 3-tab asphalt shingles come three bundles to a square, so multiply squares by three for bundle count — then add 5–15% for waste depending on how cut-up the roof is.
Our Roofing Square Calculator does the pitch math and waste allowance for you. If you're weighing a full replacement, the Storm Damage Insurance Claim Calculator estimates what insurance might cover.
A worked example
A simple gable roof over a 1,500 sq ft footprint at a 6/12 pitch has about 1,677 sq ft of surface — roughly 16.8 squares, or about 51 bundles before waste. Add 5% for a simple roof and you'd order around 53 bundles.