AWG or American Wire Gauge is a diameter unit used predominantly in the US, while a metric mm (millimeters) is used around the world. In many cases, you will need to convert AWG to mm like this: The higher the wire AWG gauge, the less mm diameter a wire has. Example: 12 AWG wire has a diameter of over 2 mm and 20 AWG has a below 1 mm diameter.

When calclating AWG from diameter or cross sectional area, the diameter and cross sectional area are rounded to the nearest AWG equivalent values. The n gauge wire diameter d n in millimeters (mm) is equal to 0.127mm times 92 raised to the power of 36 minus gauge number n, divided by 39: dn (mm) = 0.127 mm × 92 (36-n)/39

For the same cross section, aluminum wire has a conductivity of approximately 61% of copper, so an aluminum wire has nearly the same resistance as a copper wire smaller by 2 AWG sizes, which has 62.9% of the area. A solid round 18 AWG wire is about 1 mm in diameter. An approximation for the resistance of copper wire may be expressed as follows:

AWG chart