Copper wires are categorized by their American Wire Gauge, or AWG, size. A wire's AWG size enjoys an inverse relationship with its diameter; the lower the AWG, the thicker the wire and the heavier the current load it is able to carry. Conversely, a higher AWG indicates a thin, lowcapacity copper wire. AWG tables provide a handy reference that tell you the diameter of any copper wire, given its AWG category. If you don't have a table on hand, you can still find the diameter of a copper wire with a few calculations.
Things You'll Need
 AWG Table

Realize that 1 AWG = 289.3 thousandths of an inch, 5 AWG = 181.9 thousandths of an inch and 10 AWG = 101.9 thousandths of an inch. When reading an AWG table, notice that diameter is given in terms of "mils," which stands for thousandths of an inch.

Remember that copper wire diameters increase and decrease by a factor of two every six gauges, three every 10 gauges, 10 every 20 gauges and 100 for every 40 gauges.

Use 50 AWG = 1 mil as a base point. Using the general formula from Step 2, you can easily determine that 30 AWG has a diameter of 10 mil (50  30 = 20 and 10 mil every 20 gauges yields 30 AWG = 10 mil diameter).
References
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