Roof Calculator Guide
Understanding Roof Calculations
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.
Roof Area = House Footprint × Pitch Multiplier × Overhang Factor
Squares Needed = Roof Area / 100
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!
Common Roof Pitches
Low Slope
2/12 to 4/12
Easy to walk on. Common on porches and ranch styles.
Medium Slope
5/12 to 9/12
Standard residential. Walkable with caution.
Steep Slope
10/12 and up
Requires safety harness. Historic or A-frame styles.