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Roofing Calculator

Estimate the surface area of a gable roof from the building footprint and pitch, then the squares and bundles of shingles to order.

About Roofing Calculator

A pitched roof has more surface than the floor it covers. For a simple gable roof the sloped area equals the footprint, including overhangs, divided by the cosine of the pitch angle. Roofers in North America order shingles by the square, which is 100 square feet, and standard three-tab shingles come three bundles to a square. This estimate adds your waste allowance. Hips, valleys, and dormers need more material than a plain gable.

How to use Roofing Calculator

  1. Fill in "Units", "Building length", "Building width" and "Roof pitch", and the other options.
  2. The result appears below and updates as you type.
  3. Copy the result with the copy button, or download it as a file where that is offered.

Questions about Roofing Calculator

How do I convert a pitch such as 6 in 12 to degrees?

Take the arctangent of rise divided by run. A 6 in 12 pitch is arctan(6 ÷ 12), about 26.6 degrees. A 4 in 12 pitch is about 18.4 degrees, and 12 in 12 is exactly 45 degrees.

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