Gauge is a system of numbers used to indicate the wire size. It is also known as the American Wire Gauge (AWG). The largest wire using the gauge system is 0000. This largest size has a diameter of 0.46" (460 mils). Stepping down through smaller size wires, next is 000, then 00, 0, 1, 2, 3, . AWG extends beyond 40 gauge. A 40 gauge wire is about 0.003" (or 3 mils) in diameter.

With the AWG system, the higher the gauge number, the smaller the wire. 0 gauge is often referred to an "ought gauge," 00 as "double-ought," etc.

Cross sectional area is changed about 26% with each gauge (also, cross sectional area doubles with every three sizes). The diameter of a wire doubles with every six sizes. Resistance doubles for each three steps higher in gauge number.

The gauge of a wire needs to be matched to the amount of current that is required by the component connected by that wire. The current requirement is a specification given by the manufacturer of the component.