Roofing is measured in "squares," a unique trade term that simplifies large numbers. One "square" equals 100 square feet of roof area. Calculating your roof size involves not just the footprint of your house, but the slope (pitch) of the roof, which significantly increases the surface area.

The Pitch Multiplier

A flat roof has the same area as the floor below it (plus overhangs). But as the roof gets steeper, the area grows. We use a "pitch multiplier" to account for this.

For example, a 4/12 pitch (common for ranch homes) has a multiplier of ~1.054. A steep 12/12 pitch (45-degree angle) has a multiplier of 1.414—meaning the roof area is 41% larger than the house footprint!