This calculator is used for determining approximate wire gauge/size based on the length of the wire (in Feet) and the current (in Amps) in general car audio applications. When doing automotive wiring, it is important to use the proper gauge wire for the amplifier requirement. As a rule, the smaller the diameter of the wire the higher the resistance and thus lower current capability over a given length. It is almost always OK to use a larger gauge wire. When in doubt, go up a gauge. Other factors can affect the capacity of wire besides the length, and this includes the wire material (OFC vs CCA) if it is in a hot environment, duration of load, etc.