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Roofing Shingle Calculator

Enter the roof's footprint and pitch. We convert the footprint to true roof surface with the standard slope factor, then into squares and bundles, waste included.

Diagram of roof pitch showing the rise over the run and the sloped roof surface
Roof area grows with pitch. The slope is longer than the flat run beneath it.

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Enter your measurements

How shingle quantities are calculated

Roofing is sold by the square: 100 sq ft of roof surface. Standard shingles pack 3 bundles to a square (a bundle covers ~33.3 sq ft); heavyweight architectural shingles run 4–5 bundles per square. Pick your product's rate below.

The catch is that a roof's surface is bigger than its footprint. Roofers correct with a pitch (slope) factor: √(1 + (rise ÷ 12)²). The published table (4/12 → 1.054, 6/12 → 1.118, 8/12 → 1.202, 12/12 → 1.414) is exactly that formula, and it's what this calculator uses. True area = footprint × factor; bundles = area (plus waste) ÷ sq ft per bundle.

Waste: 10% covers cutting and starter courses on a simple gable roof; use 15% for hips, valleys and dormers. Measure the footprint including eaves overhangs, or measure each slope directly on the roof and use the 0/12 (flat) pitch to get bundles from a known area.

Sources

The figures behind this calculator come from published manufacturer data and industry standards:

Worked examples

30 × 40 ft roof, 6/12 pitch

1,200 sq ft × 1.118 = 1,342 sq ft (13.4 squares), +10% waste, 3 bundles per square.

Buy 45 bundles

24 × 36 ft roof, 4/12 pitch

864 sq ft × 1.054 = 911 sq ft (9.1 squares), +10% waste.

Buy 31 bundles

20 × 28 ft roof, 8/12 pitch, heavyweight

560 sq ft × 1.202 = 673 sq ft, +15% waste, 4 bundles per square (25 sq ft each).

Buy 31 bundles

Frequently asked questions

How many bundles of shingles do I need for 1,200 sq ft?
If 1,200 sq ft is the true roof surface: 12 squares × 3 bundles = 36 bundles, or 40 with 10% waste. If 1,200 sq ft is the house footprint, pitch adds more. At 6/12 it's really 1,342 sq ft and 45 bundles with waste.
How many bundles are in a square of shingles?
Three for standard three-tab and most architectural shingles. Each bundle covers about 33.3 sq ft. Heavyweight and premium lines pack 4 or 5 bundles per square so the bundles stay liftable; the count is printed on the wrapper.
How do I find my roof pitch?
Put a level 12 in out from the roof edge (or use a pitch-finder app on the slope) and measure the vertical rise over that 12 in of run. A rise of 6 in over 12 in is a 6/12 pitch. From inside the attic, measure against a rafter the same way.
Does this include ridge cap and starter shingles?
The waste allowance covers starter courses on simple roofs. Ridge cap is sold separately by the linear foot (or cut from three-tab shingles, ~one bundle per 30–35 ft of ridge). Measure your ridge and hip lengths and add it on top.
What about underlayment and nails?
Budget separately: a roll of synthetic underlayment covers ~1,000 sq ft (felt ~360–430 sq ft per roll), and roofer's rule is about 2.5–3 lb of 1-1/4 in roofing nails per square with a 4-nail pattern.

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Estimate disclaimer: results are planning estimates based on standard manufacturer yields and coverage figures. Site conditions, product choice and installation method change actual quantities. Verify before you buy, and follow local building code for structural work. This tool does not replace professional engineering advice.

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