Finding Proper Wire Size


It is very important to use the proper wire size in a system. Besides losing points at competitions, too small of a wire could heat up and catch your car on fire.

First you need to calculate the maximum total system current draw. It is done as follows:

Total RMS power x 2 = Total power usage

Total power usage/battery voltage = Current draw

1. Find out how many watts RMS your amps will deliver
2. Summarize for total RMS power
3. Multiply the total RMS power by 2 (since most amps are only 50% efficient)
4. Divide the total RMS power by 13 (average battery voltage)
5. That figure is your total current draw (at the impedance where the total RMS was said to be)
6. Find out how long the power cable will be, and then find the appropriate wire size

Now keep in mind that if you go into lower impedance, say 2 ohms, the current draw will be twice as much!

Cable length (meters*) and thickness (gauge)

Total current
draw in Amperes

0-1.2 m 1.2-2.0 m 2.0-3.0 m 3.0-4.0 m 4.0-5.0 m 5.0-5.8 m 5.9-6.7 m
0-20 A 14 ga 12 ga 12 ga 10 ga 10 ga 8 ga 8 ga
21-35 A 12 ga 10 ga 8 ga 8 ga 6 ga 6 ga 6 ga
36-50 A 10 ga 8 ga 8 ga 6 ga 6 ga 4 ga 4 ga
51-65 A 8 ga 8 ga 6 ga 4 ga 4 ga 4 ga 4 ga
66-85 A 6 ga 6 ga 4 ga 4 ga 2 ga 2 ga 2 ga
86-105 A 6 ga 6 ga 4 ga 2 ga 2 ga 2 ga 2 ga
106-125 A 4 ga 4 ga 4 ga 2 ga 2 ga 0 ga 0 ga
126-150 A 2 ga 2 ga 2 ga 2 ga 0 ga 0 ga 0 ga

* 1 foot = 0.3048 meters. So if your cable is 15 feet long, it is 15 * 0.3048 = 4.57 meters.

Gauge Square millimeters (mm2)
14 ga 2.5 - 3 (mm2)
12 ga 3 - 4 (mm2)
10 ga 6 - 8 (mm2)
8 ga 8 - 13 (mm2)
6 ga 13 - 19 (mm2)
4 ga 21 - 27 (mm2)
2 ga 27 - 35 (mm2)
0 ga 35 - 45 (mm2)
1/0 ga 45 - 54 (mm2)