American Wire Gauge (AWG)

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Wire size is expressed in circular mils(CM). A mil is one-thousandth of an inch. In the United States, the American Wire Gauge is used. It is a scale of even numbers that start with the number 40 and descend. The cross-sectional area becomes larger as the numbers on this scale get smaller. 

For wires larger than No.2 wire, a scale of 1/0, 2/0, 3/0 and 4/0 is used. For even larger wires, thousands of circular mils is used –MCM or Kcmil

AWG Conversions
Copper conductor size conversions are determined using;

Circular mils = sq in. x 1,273,240 = sq mm x 1,973.5

For conductor cross-sectional forms other than circular, where S is the cross-sectional area in square inches, the conversions are:

The table below shows a quick guide to AWG wire conversions: