Roofing calculator
Squares and bundles of asphalt shingles from your roof footprint and pitch — plus underlayment rolls and nails.
Roof details
How this is calculated
Start with the roof’s ground footprint: length × width. Pitch increases the actual surface area — a 6/12 pitch adds about 12%, a 12/12 pitch adds about 41%. That surface area is increased by a waste factor (10% for a simple gable, 15% with hips or valleys, 20% for complex roofs with dormers). Roofing is sold by the square (100 sq ft). Bundles depend on the product — most asphalt shingles pack 3 bundles per square. Underlayment is estimated at one 4-ft × 250-ft roll (~10 squares of coverage) per 10 squares of roof, and nails at roughly 2–2½ lb per square for hand-nailing.
How many shingles for a 40×24 roof?
At a common 6/12 pitch with 15% waste, that footprint needs about 12 squares, or roughly 36 bundles of standard asphalt shingles.
What is a roofing “square”?
One square covers 100 square feet of roof surface. It’s the unit suppliers price by, regardless of whether you buy 3-tab or architectural shingles.
Should I measure the roof or the house footprint?
Footprint (length × width on the ground) is fine if you know the pitch — this calculator converts it for you. If you can safely measure the actual slope length of each plane, use those areas and set pitch to 4/12 (near-flat factor) so you don’t double-count slope.
Once you know how much to order
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Architectural asphalt shingles
~3 bundles per square; check coverage on the package.
View on Home DepotSynthetic underlayment roll
Typically covers about 10 squares per roll.
View on Home Depot