Roof Square Footage Calculator
Convert building footprint and roof pitch into estimated roof surface area and roofing squares.
Planning estimate only. Confirm supplier quantities, local code requirements, and field measurements before ordering or construction.
Reviewed September 6, 2026Runs in your browser
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How this calculator works
Roof area = footprint × pitch factor × (1 + waste), where pitch factor = √(1 + (rise/12)²).
Worked example
An 1,800 sq ft footprint with a 6:12 roof pitch produces about 2,214 sq ft after 10% waste.
Sources & assumptions
The calculator converts horizontal footprint to sloped roof area using the entered pitch. Complex roofs, overhangs, dormers, valleys, and intersecting sections should be measured separately.
Frequently asked questions
Why is roof area larger than house area?
Slope adds surface area. Overhangs and roof complexity can increase it further.
What waste factor should I use?
Ten percent is a common planning starting point. Complex roofs can require more.