Roof Area Calculator
How to calculate roof area
- Choose meters or feet, and enter the building's length and width and the overhang on each side.
- Choose the roof shape and enter the pitch in degrees, as rise per 12, or as a percent.
- The roof area appears with the material needed including waste, the rafter length and the ridge height.
Frequently asked questions
How is the area worked out?
The footprint including overhangs is divided by the cosine of the roof angle. With the same pitch on every slope this holds for gable, hip and shed roofs alike, because each part of the roof is the plan area beneath it tilted by the same angle.
What is a roofing square?
In North America roofing is sold by the square: 100 ft² of roof surface.
How much waste should I allow?
About 10% for a simple gable roof and 15% or more for hip roofs and roofs with valleys and dormers, where more material is cut off.
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