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1 circular mil = 1 mil x 1 mil
a=d2
so if a wire has a diameter of 80 mils, it has an area of 6400 circular mils.
.000025 circular inches = 25 circular mils
1 Circular mil = 0.7854 x 10-6 Square InchConveter:http://www.unitconversion.org/area/circular-mils-to-square-inchs-conversion.htmlInformation from:http://www.engineeringtoolbox.com/mil-circular-mil-area-d_817.html
By the diameter of the wire.
Google wire circular mil.