How the roofing calculator works
The ground footprint doesn't equal roof area — the slope makes it bigger. We multiply your footprint by a pitch factor to get true slope area, add 10% for waste and starter/hip/ridge, then convert to squares (100 sq ft each). Standard 3-tab and architectural shingles run about 3 bundles per square.
Understanding pitch
Pitch is the rise over a 12-inch run. A 6/12 roof rises 6 inches per foot. Steeper roofs have more surface area per square foot of footprint — and cost more to install. If you already measured the actual sloped area, pick "Flat / already measured."
What's a roofing square?
A square is 100 square feet of roof — the standard unit roofers and suppliers price by. Shingles are sold in bundles, with roughly 3 bundles covering one square.