Roofing Calculator: Squares and Shingle Bundles
Enter the footprint of the building, the roof pitch and the eave overhang. The calculator finds the sloped roof area, converts it to roofing squares and rounds up to whole shingle bundles at 3 bundles per square. After switching units, re-enter your measurements.
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Formula
footprint = (length + 2 x overhang) x (width + 2 x overhang)slope factor = sqrt(1 + (pitch / 12)^2)roof area = footprint x slope factorsquares = roof area (sq ft) / 100bundles = round up (squares x (1 + waste %) x 3)
Metric inputs are converted with 1 ft = 0.3048 m exactly, so 1 sq ft = 0.09290304 m2.
Worked example
A 40 ft by 30 ft building with a 1 ft overhang, a 6:12 pitch and 10% waste:
- Footprint with overhang: 42 x 32 = 1,344 sq ft.
- Slope factor: sqrt(1 + 0.5^2) = 1.118034.
- Roof area: 1,344 x 1.118034 = 1,502.64 sq ft (139.60 m2), which is 15.03 squares.
- With 10% waste: 15.03 x 1.10 = 16.53 squares.
- Bundles: 16.53 x 3 = 49.59, rounded up to 50 bundles.
Assumptions
- One uniform pitch on every roof plane, with the roof covering the footprint plus the overhang on all four sides.
- 3 bundles per square (100 sq ft each). Some products differ, so check the pack coverage.
- Waste covers cuts and mistakes. Starter strips, ridge caps, underlayment and flashing are ordered separately.
Frequently asked questions
How many shingle bundles are in a roofing square?
A roofing square covers 100 square feet, and most architectural and 3-tab shingles are sold at 3 bundles per square. A roof of 16.5 squares therefore needs 16.5 x 3 = 49.5, which rounds up to 50 bundles.
How is roof area calculated from the footprint and pitch?
Add the overhang to each side of the footprint, multiply length by width, then multiply by the slope factor sqrt(1 + (pitch / 12)^2). For a 40 x 30 ft building with a 1 ft overhang and a 6:12 pitch that is 42 x 32 x 1.118 = 1,502.6 sq ft.
How much waste should I allow for shingles?
10 percent suits a plain gable roof. Hips, valleys, dormers and cut-up roofs often need 15 percent or more, and the starter and ridge courses are extra. Check the manufacturer's coverage for your product.
Does this work for hip roofs and complex roofs?
It assumes every roof plane has the same pitch and the roof covers the whole footprint plus overhang, which is exact for simple gable and hip roofs. Add waste for valleys, dormers, chimneys and skylights, and have a roofer confirm the final order.