Roofing Calculator
Enter your roof size to get the shingles you need in squares and bundles, plus an estimated cost. Waste is included.
Shingles needed
Estimated cost
How to calculate roofing shingles
Roofers measure in squares, and one square is 100 sq ft. Find the roof area, add waste, divide by 100 for squares, then multiply by 3 for bundles, since 3 bundles normally make one square.
Formula: squares = roof area (sq ft) × (1 + waste %) ÷ 100, and bundles = squares × 3, rounded up
Worked example: 40 ft × 30 ft roof
Roof area = 40 × 30 = 1,200 sq ft. Add 10% waste: 1,320 sq ft. Divide by 100: 13.2 squares. Bundles: 13.2 × 3 = 39.6, rounded up to 40 bundles.
Flat or sloped?
Measure the slope length for a pitched roof, not the flat footprint on the ground. A steep roof can be much larger than its footprint.
How much waste?
Simple gable roofs need about 10% extra. Roofs with hips, valleys and dormers need 15% or more, because every cut wastes a shingle.
Common roof sizes
Cost tips
Prices on this page are editable estimates, not quotes. Get 2 to 3 local quotes before you buy, and ask if delivery is included. Delivery, tax and waste can change the total a lot. Order a little extra for cuts and breakage, and confirm final quantities with your supplier or a qualified professional.
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Frequently asked questions
How many bundles do I need for a 40x30 roof?
A 40 ft by 30 ft roof needs 13.2 squares with 10% waste, which is 40 bundles at 3 bundles per square.
What is a roofing square?
One square is 100 sq ft of roof area. Shingles are sold by the square, and usually 3 bundles make one square.
How much waste should I add?
Add 10% for simple roofs and 15% or more for roofs with hips, valleys and dormers.
Does this work for a pitched roof?
Measure the slope length, not the flat footprint. For a pitched roof, use the sloped width instead of the ground width.
Does this include underlayment and ridge caps?
No, this counts shingle bundles only. Underlayment, ridge caps, flashing and nails are extra.
Are the prices accurate?
Prices are editable estimates. The defaults are typical US figures, and your local price can be higher or lower.