You enter the roof footprint length and width in feet and select the roof pitch. The tool multiplies the flat footprint area by a pitch multiplier derived from the Pythagorean theorem (√(1 + (rise/12)²)), divides by 100 to get squares, multiplies by 3 for bundle count, and uses the roof length as ridge cap footage. It assumes a simple gable roof with one ridge and does not account for hips, valleys, dormers, or waste.
A square is a roofing industry unit equal to 100 square feet of roof area. When a contractor says your roof is "30 squares," it means 3,000 sq ft of actual roof surface. Shingles, underlayment, and other materials are all priced and ordered per square.
For a simple gable roof, 10% waste is typical. Hip roofs, roofs with dormers, skylights, or complex angles may need 15–20% extra for cuts and fitting. Discuss waste allowance with your contractor before ordering.
Roof pitch is the rise in inches per 12 inches of horizontal run. You can measure it from the attic with a level and tape measure: hold a level horizontally, mark 12 inches, and measure straight up to the underside of the rafter. That vertical distance is your pitch number.
The area and square calculations apply to any roofing material, but the "bundles" output assumes standard three-tab asphalt shingles. Metal panels, tiles, and roll roofing are sold in different units and quantities.
This calculator assumes a simple rectangular footprint with one ridge. For hip roofs, L-shaped houses, or roofs with multiple sections, calculate each rectangular section separately and add the results together. Add extra waste for hip and valley cuts.
Estimate only. Results reflect your inputs and standard formulas. Double-check important decisions independently.