How roof square footage is calculated
The building footprint is multiplied by a slope factor based on the roof pitch. This converts horizontal footprint area into estimated sloped roof area.
Roof area example
A building footprint of 40 feet by 30 feet has 1,200 square feet of horizontal area. A pitched roof has more surface area than this footprint, so the pitch factor increases the result.
Why roof pitch changes area
As roof slope becomes steeper, the sloped surface becomes longer even though the horizontal building dimensions stay the same.
This calculator is most suitable for simple roof forms. Dormers, valleys, multiple roof sections and unusual geometry should be measured separately.
Frequently asked questions
What does a 6:12 roof pitch mean?
It means the roof rises 6 inches for every 12 inches of horizontal run.
Is roof square footage the same as building footprint?
Not usually. A sloped roof has more surface area than its horizontal footprint.
What is a roofing square?
One roofing square equals 100 square feet of roof area.
Should waste be included?
A waste allowance is commonly included for cutting, overlaps and roof complexity.