How to determine the gauge (AWG) of automotive wire. Make a small cut about 1/2″ long in the wire insulation and remove it. Count the individual strands of copper that make up the wire. Next, use a micrometer and measure one of the strands. Now use the following chart to determine the gauge of your automotive wire. 7/ .028 = 20 AWG (7 strands that measure .028 each equals 20 gauge). 16/ .030 = 18 AWG.