Roofing Calculator
Estimate roofing materials from the building footprint and roof pitch. The calculator returns the sloped roof area, roofing squares, bundles of shingles and rolls of underlayment — with waste allowance built in.
Enter building and roof details
Enter roof dimensions, then press Calculate roofing.
Roofing formulas
Roof pitch multiplier = √(1 + (rise/run)²)
Sloped roof area = footprint area × pitch multiplier
Roofing squares = sloped area ÷ 100 (imperial) or ÷ 9.29 (metric)
Bundles of shingles = roofing squares × 3 (standard 3-tab shingles)
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Frequently asked questions
One roofing square equals 100 square feet of roof surface (about 9.29 m²). Roofing materials in North America are sold by the square — a typical asphalt shingle bundle covers 1/3 of a square, so three bundles make one square.
A sloped roof has more surface than the flat footprint it covers — like a ramp has more surface than the ground it stands on. The steeper the pitch, the greater the multiplier. A 5/12 pitch adds about 8% to the footprint; a 12/12 pitch adds about 41%.