AWG is a standard denoting wire diameter, whereas the metric conductor sizes according to standard IEC 60228 describe a wire in terms of its cross-sectional area, rather than its diameter, because the cross section is directly proportional to its strength, weight, and resistance. The cross-sectional area is also roughly proportional to the maximum current-carrying capacity of a wire.

There is, however, an equivalent unit of area for comparing metric to AWG wire sizes: the circular mil. It is the equivalent area of a circle whose diameter is .001 (10-3) inch, or approximately .7854 millionths of a square inch
(or 2.5 × 10-7 times pi). To convert millimetres squared approximately to circular mils multiply by 1974 or divide by
0.0005067. Conductors larger than 4/0 AWG are generally identified by the area in thousands of circular mils (KCMIL), where 1 KCMIL = 0.5067 mm².