Roofing calculator

A roofing square is a unit of roof area equal to 100 sq ft. It is the way shingles are counted and sold. Three bundles of shingles cover one square.

A steeper roof has a larger sloped surface than a flatter one over the same footprint. The pitch multiplier accounts for this, so the calculator scales the flat footprint area up by a factor you get when you square the pitch divided by 12, add 1, and take the square root. The multiplier grows as pitch rises, which means more shingles for the same house footprint.

The calculator estimates felt underlayment separately from shingles. One roll covers four roofing squares, so you divide the total roof area in squares by four to get the number of rolls. For the 50-bundle example, the roof area is about 15 squares, which comes to roughly four rolls.

A 12 by 16 foot shed with a 4/12 pitch and no overhang needs about 7 bundles of shingles. That covers roughly 202 square feet of roof area. The total includes a 10% waste allowance. If your shed has different measurements or a different pitch, the count will be different.

About 74 bundles for a 2,000 square foot footprint house with a 6/12 pitch and no overhang. The roof area is about 2,236 square feet. That count includes a 10% allowance for cutting and waste. The footprint is the ground-floor area; the roof area is larger because of the pitch.

There is no standard number of shingles in a bundle; it varies by product. The constant is coverage: one bundle covers about 33 square feet of roof, which is one third of a roofing square.