Square footage of a circle:
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Find the center point of the circle.
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Measure from that point to the edge of the circle to determine the radius.
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Multiply the radius by itself.
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Then multiply that number by PI (3.14) to find the area of your circle.
So 275 X 275 X 3.14 = 237,462.5 mm
which equals 2.556025 square feet
I used this to convert mm to feet
http://www.ilpi.com/msds/ref/areaunits.html