Roofing Calculator
Estimate roof area, roofing squares, and the number of shingle bundles needed from the building footprint and roof pitch.
How it works
Roof area formula
Footprint = Length × Width Pitch multiplier = √(rise² + 12²) / 12 Roof area = Footprint × Pitch multiplier Squares = Roof area ÷ 100
A sloped roof covers more surface than the building footprint beneath it. The pitch multiplier converts the flat footprint into the true sloped area: a 6:12 roof is about 1.118× its footprint. Roofers measure in 'squares' of 100 square feet, and asphalt shingles usually come three bundles to a square.
Worked example
A 40 ft × 30 ft house (1,200 ft² footprint) with a 6:12 pitch has a roof area of about 1,342 ft². With 10% waste that's 1,476 ft² ≈ 14.8 squares, or about 45 shingle bundles.
Frequently asked questions
What is a roofing square?
A square is 100 square feet of roof area — the standard unit roofers use to quote materials and labor. A 2,000 ft² roof is 20 squares.
How does roof pitch affect the amount of material?
Steeper roofs have more surface area for the same footprint. A flat roof equals its footprint, a 6:12 pitch is about 12% more, and a 12:12 (45°) pitch is about 41% more.
How much waste should I add?
10% is typical for a straightforward gable roof. Add 15% or more for roofs with many hips, valleys, or cut-up shapes where more shingles are trimmed and discarded.