Before we proceed to discuss the Types of Wires For Electrical Outlets let briefly consider how wire are being measured. The gauge of wire used for electrical outlets and circuits is a measure of the diameter of the wire using a standard wire gauge.  Therefore, a larger gauge of wire refers to a wire with a small cross-sectional area or small-diameter and vice versa; this is because the concept of gauge is obtained from the size or number of wires you can fix through a standard opening use worldwide to measure the diameter of a wire.     As shown above in the image the diameter for a standard 12-gauge copper wire is usually 2.05 mm, while that of 14-gauge copper wire is 1.63 mm.