Cable Gauge Chart

To determine the approximate current draw (in amperes) of your amplifier (or amplifiers), you must calculate first the total power of each amp (multiply the number of channels by the number of RMS watts per channel). If you have multiple amps, add up the total power figures to arrive at a grand total. Next, double your grand total power figure. Then, divide by 13.8.

The resulting figure is your system's approximate current draw. Compare this number to the numbers in the "Amperes" column in the chart below. Cross-reference with the cable length (the distance from your battery to the amp mounting location) to determine which gauge of cable you need.

Once you have estimated the total amperage of your system using the described formula, determine the proper power and ground wire gauge from this chart based on the length of power cable your installation requires.

A more detailed explanation

Here is an explanation about the formula we use, in case you want more details. Calculating the amp's total power is straightforward, but the other two parts can be confusing.

First of all, why do we double the total power figure? That's because the typical analog amplifier is about 50% efficient. That means about half of the power it generates is turned into audio output while the other half of the power is lost as heat. So if your amplifier is putting out 400 watts, it's actually using enough electrical power to generate about 800 watts of power, and the amp's wiring needs to be big enough to handle that draw. (Digital amps are much more efficient in comparison, but it's still safest to go with the larger wire size.)

And the 13.8? Yes, vehicles have a 12-volt electrical system, but we're assuming that the vehicle is running, which means its alternator is generating additional current, which typically bumps up the voltage to about 13.8 volts. This is a better real-world representation of the vehicle's electrical supply. Dividing by 12 results in a larger number, which could point to a larger wire gauge, but it's often in the same color range in the chart.

Finally, according to our tech support guys, the primary performance limitation in most amplifier installations is in the current delivery — either a weak ground or insufficient wire gauge. Installing too small of a wire gauge results in poor performance, potentially shorter service life of connected components (your amplifier and speakers), and a potential safety hazard.

On the other hand, installing too large a wire gauge doesn't really have a downside, but there is the potential for better performance. Obviously, there's no need to buy 2-gauge wiring when 10-gauge will do. That kind of overkill would be a waste of money. But if the chart could lean either way between two sizes, going with the larger wire size would be the smart choice.