Roofing Calculator FAQ

One roofing square equals 100 square feet of roof area. It is the standard unit used by roofing contractors for quoting material quantities and pricing. If your roof is 2,000 sq ft, that is 20 squares. Using squares rather than square feet makes it easier to estimate bundles and compare contractor quotes.

Roof pitch is the rise in inches for every 12 inches of horizontal run. For example, a 6/12 pitch means the roof rises 6 inches for every 12 inches it runs horizontally. You can measure this with a level and measuring tape, or estimate it from the roof slope using the pitch selector.

Standard asphalt shingles usually take about 3 bundles per square. Each bundle covers roughly 33 sq ft. However, architectural shingles may require 4 bundles per square depending on the exposure. The default for the calculator is 3 bundles, and you can adjust this in the Materials mode if your product differs.

10% is common for simple roofs with few penetrations and straight ridges. Complex roofs with valleys, dormers, hips, or multiple gables often need 15% or more. If you are using a pattern-matched material like tile, consider 15-20% waste to account for cut pieces.

Cost depends on roof size, material, labor, and disposal. A typical asphalt shingle roof on a 2,000 sq ft home runs $7,000-11,000 installed (materials, labor, disposal). Metal roofs are $12,000-24,000. The Cost mode in this calculator breaks down each component so you can see exactly where the money goes.

Some roofs can accept one additional layer of asphalt shingles, but most building codes now limit roofs to two layers total. A full tear-off is usually the better option because it allows inspection of the decking, proper installation of underlayment, and a longer-lasting result. The calculator's cost estimate does not include tear-off by default.

Underlayment is a water-resistant or waterproof barrier installed directly on the roof deck before the shingles—it provides secondary protection against wind-driven rain. Drip edge is a metal flashing installed along the eaves and rakes to direct water away from the fascia and into the gutters. Most building codes require both.