This is a simple calculator for determining approximate wire gauge/size based on the length of the wire (in feet) and the current (in amps). After you enter in your data, the table will guide you to the wire gauge that is appropriate by checking the box under 'Size OK'.

Visit our Cables and Accessories category to shop for cable and wire by the foot.

Enter in your Parameters and Press Calculate
Amperage Enter Maximum Circuit Amperage
Wire Length
Enter Total Wire Length in Feet
Percent Drop
Wire Calculator
Wire GaugeEnd VoltageMax LengthSize OK
22 Gauge
20 Gauge
18 Gauge
16 Gauge
14 Gauge
12 Gauge
10 Gauge
8 Gauge
6 Gauge
4 Gauge
2 Gauge
1 Gauge
0 Gauge (1/0)
00 Gauge (2/0)

The voltage drop value will vary depending on your application. We prefer using the 2% mark as a conservative value and to ensure delivering full potential to any needed electrical source. From what it looks like in many automotive applications a 5% or more voltage drop is more common.

As a general 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 about the load go up a gauge. Other factors can affect the capacity of wire besides the length, and this includes if it is in a hot environment, duration of load, stranded vs. solid wire, wire plating, etc. Check out Wikipedia for more info on wires (AWG, Brown and Sharpe), gauges, and the math.

How to use this calculator:

  • This is for a ONE WAY wire with the ground assumed to be the car chassis. If two wires are needed to complete the circuit, calculate for the total length of wire used for both legs. To use the calculator, enter the Maximum Current in Amps of the circuit, and the Length of the Wire, and operating Voltage. Typically most automotive systems run at 13.8V, but you can select 6, 12, 13.8 (Default) or 24 volts. If the wire gauge is OK to use it will have a 'Check Mark' on the same line. The 'Max Length' indicates the maximum length of wire of that gauge that can be use at the given values you entered.
  • We believe the table to be an accurate general guide for MOST applications, however you agree to use at YOUR OWN RISK. By using our wire calculator, you agree to hold us harmless and you understand that this calculator is merely a guide and help, but not an absolute authority, therefore we recommend you have a professional or an engineering company perform the calculations in your application.