American Wire Gauge ( AWG )
American Wire Gauge (AWG) is a U.S. standard set of non-ferrous wire conductor sizes used since 1857. The "gauge" means the diameter. Non-ferrous includes copper and also aluminum and other materials, but is most frequently applied to copper household electrical wiring and telephone wiring. The higher the gauge number, the smaller the diameter and the thinner the wire.
Since thicker wire carries more current because it has less electrical resistance over a given length, thicker wire is better for longer distances. Increasing gauge numbers denote decreasing wire diameters. This gauge system originated in the number of drawing operations used to produce a given gauge of wire. Very fine wire (for example, 30 gauge) required more passes through the drawing dies than 0 gauge wire did. So when you saw such numbers like this : 28AWG/28AWG printed on a USB cable, you now know they are referring to the wire inside the cable.
1. When the cross-sectional area of a wire is doubled, the AWG will decrease by 3.
(e.g., Two No. 14 AWG wires have about the same cross-sectional area as a single No. 11 AWG wire.)
2. When the diameter of a wire is doubled, the AWG will decrease by 6.
(e.g., No. 2 AWG is about twice the diameter of No. 8 AWG.)
3. A decrease of ten gauge numbers, for example from No. 10 to 1/0, multiplies the area and weight by approximately 10, and reduces the electrical resistance (and increases the conductance) by a factor of approximately 10.
4. 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 2 AWG sizes smaller, which has 62.9% of the area.