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Roofing Shingles Calculator

Footprint and roof pitch in; roof area, squares and shingle bundles out.

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Your project

Shingles needed

Enter your numbers above.

Measure the roof, not the house, when you can

Dormers, porch roofs and garage tie-ins make footprint-based estimates run short. If you can get on the roof safely, or pull a satellite measurement report, measure each plane directly. Use this calculator as a check, and lean toward the higher number when ordering.

How roof area and shingle bundles are calculated

Start with the house footprint plus the overhang on every side. A sloped roof covers more area than that flat plan, so the calculator multiplies by a pitch factor = √(1 + (rise ÷ 12)²). A 6/12 roof has a factor of about 1.118, meaning it has about 12% more surface than its footprint. This works for gable and hip roofs alike, since every plane shares the same pitch.

Roofing is sold by the square, which is 100 sq ft of roof. Most architectural and 3-tab shingles come three bundles to the square, so bundles = roof area × (1 + waste %) ÷ 100 × 3, rounded up. Manufacturers such as GAF and Owens Corning suggest about 10% waste for plain gable roofs and 15% or more for hips, valleys and dormers, where every edge is cut.

Underlayment is figured on the roof area without waste. Synthetic underlayment rolls commonly cover 10 squares; 15 lb felt covers about 4 squares per roll. Starter strip and hip-and-ridge cap are separate products sold by the linear foot, so measure your eaves, rakes, hips and ridges for those.

Where these numbers come from

The formulas and default values in this calculator are based on:

  • GAF and Owens Corning shingle installation and estimating guides (3 bundles per square, waste allowances by roof type)
  • standard roof-pitch multiplier from right-triangle geometry

These are planning estimates. Check product labels, your local building code, and a licensed contractor before you buy materials or build.

Frequently asked questions

What does roof pitch 6/12 mean?

It means the roof rises 6 inches for every 12 inches it runs horizontally. You can measure it from the attic with a level and tape: hold a 12-inch level flat against a rafter, then measure straight up from its end to the underside of the rafter.

Why do I need more shingles on a hip roof?

A hip roof has sloped ends instead of flat gable walls, so every hip line is a diagonal cut on both sides. Those cuts create more offcuts than a gable roof, which is why waste goes from about 10% to 15%.

Should I round up to full squares?

Order by bundles, not squares, and round up to the next whole bundle. Suppliers usually accept unopened bundles back, and running out mid-roof means a color-match gamble on a second batch.

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