Roofing Calculator

This calculator starts with your building's flat footprint area (length × width), then applies a pitch multiplier to account for the roof's slope, since a sloped roof has more actual surface area than its footprint. The multiplier is calculated as √(144 + pitch²) ÷ 12, where pitch is the rise in inches per 12 inches of horizontal run (for example, a '6/12' roof has a pitch of 6).

Roofing materials are measured in 'squares,' where 1 square covers 100 square feet. This calculator divides your total roof area (plus waste allowance) by 100 to find the number of squares, then multiplies by 3, since standard shingle bundles are packaged 3 per square.

Roof pitch is usually expressed as 'X/12,' meaning the roof rises X inches for every 12 inches of horizontal run. A 4/12 roof is fairly shallow, while a 12/12 roof is a steep 45-degree slope. Check your building plans, or measure with a level and tape measure along a section of exposed rafter.