A 12-gauge wire can carry between 15 and 20 amps for normal electrical wires. When wiring chassis, 12-gauge wire can carry a maximum of 41 amps along the metal conductor. The conductive part of a 12-gauge wire is 0.0808 inch in diameter. This gauge is found in extension cords.
The gauge number of wires gets smaller as the diameter gets larger. Every sixth gauge indicates a doubling of the diameter. For instance, a 6-gauge wire is 0.162 inch, or double that of a 12-gauge wire. One of the largest, 0000-gauge wire, is 0.46 inch in diameter. One of the smallest, 32-gauge wire, is 0.008 inch wide.