Wire gauge describes the measurement of the wire diameter or its cross-sectional area. Wire gauge is an essential measure as it determines the electrical cable's ampacity and the amount of current that it can safely carry. Moreover, it also determines the weight of the cable and its electrical resistance.

Why is Wire Gauge Important?

Knowing the wire gauge is crucial to determine whether the cable is suitable for a particular application and whether this application would be safe and effective. By knowing the wire gauge, you also learn the current-carrying capacity of the cable. This helps you to choose a cable according to the demands of your electrical circuit.

If the wire is too small or thin for an electrical circuit, it will melt and most probably cause an electrical fire. Choosing a wire that is too big for an electrical circuit is not as dangerous, however, the wire will be unnecessarily expensive for your electrical project. Since bigger wires are also heavier, the cost of the wire installation will be higher as well.

Common Types of Wire Gauge

Since the 18th century, there have been many systems in use to determine the size of the electrical cable. Currently, the three standards for determining the size of a wire that is still used are British Standard, IEC 60228, and American Wire Gauge. The biggest number of countries in the world, including the majority of the countries in Eurasia, use IEC 60228. American wire gauge, or AWG, is the system that determines the size of the wire in North America. Since we are located in the US, we use AWG for our wire measurements.

American Wire Gauge

In the United States, The terms "AWG'' and gauge are used interchangeably to describe the size of an electrical conductor. American wire gauges come in sizes from 0000 to 40. Do not let this sizing confuse you, though- the higher the gauge's number is, the smaller the diameter of the electrical cable. Likewise, the lower the number is, the bigger is the size of an electrical cable. Therefore, wire sized 2 is going to be large and heavy, whereas wire sized 32 will be small and flexible.

An important thing to note is that sizes between 14 and 2 are usually considered standard for most purposes. 

Components of a Wire Gauge

Some important components of a wire gauge that you should know are diameter, cross-sectional area, and current capacity that is measured in amps.

The lower the AWG number, the larger is the diameter of a wire. The electrical resistance of small wires is usually higher than those of large wires because there is less space for the current to escape. The diameter of an electrical wire is usually calculated in millimeters despite the fact that the metric system is not widely used in the United States. However, it is sometimes calculated in inches as well. The cross-sectional area is also commonly calculated in centimeters and millimeters. The current capacity is naturally higher in bigger wires because their large size allows them to carry more current. 

Kmil Vs. AWG

However, not all gauges of conductors used in the United States are indicated using AWG as a name for a measurement. The conductors in measurements larger than 4/0 AWG are calculated in thousands of circular mils or kmil. The older name of this MCM, or one thousand circular mils. This name is still widely used in the USA. For this reason, the conductors sized between 250 and 1000 are called 250 MCM and 1000 MCM, and not 250 AWG. Do not be confused, though, the size of these conductors is still determined using American standards.

Wire Gauge Chart

Here is the chart that converts AWG into cross-sectional diameter of the electrical wire:

How Do I Choose Electrical Wire Gauge?

The wire gauge you need depends on the many specifications of your electrical project, but the most important measure that determines the size of the electrical wire that you need is ampacity. 

It may be best to contact your electrician or cable-selling company to determine the wire gauge you need for your electrical project; however, there are also some standard rules for wire gauge applications that may help you. Mind that the size of the wire should depend on the ampacity of your electrical circuit.

As a rule:

• 18 AWG wires are used in low-voltage lighting systems
• 16 AWG wires are used in extension cords with an ampacity of 13 Amps
• 14 AWG wires are perfect for standard lighting circuits
• 12 AWG wires are applied in AC power plugs and sockets within the home and low-voltage air conditioners
• The wires in gauge ten or lower are used in different home equipment. Aim for 10 AWG for 30 Amps, 6 AWG for 50 Amps, and 4 AWG for 60 Amps.

How To Check For a Wire Gauge Number?

If you wish to know the size of the cable, the first suggestion is to look at the cable directly. The small text with a wire gauge is written on the insulation most of the time. 

If you cannot find the text, you can determine the size of a cable manually by cutting the wire perpendicularly and measuring the cross-sectional area of the cable. Remember that the diameter of the insulation should not be included in this measurement.

After you measured the diameter of a wire, you should divide it by .46, use a calculator to determine the logarithm of this number, and divide the logarithm by -.050305. This final number minus three is the size of your wire in AWG.

If cutting the wire and calculating the gauge is not an option for you for any reason, look for your cable order summary or contact your seller or electrician to help you determine the size of your cable.