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How to Choose an Extension Cord Gauge – Sizing & Amperage Chart

Many of us use extension cords in our households, offices, etc. whether it is for a tool, appliance, or any electrical instrument. There are a variety of cords that you can choose from, but the question is, what gauge extension cord do I need? If you too have this question, you will get every possible explanation regarding each. Choosing the wrong one may lead to overloading or short circuit even.

What Gauge Extension Cord Do I Need?

Since there is a variety of extensions available, there are certain factors that you can consider before choosing one.

1. Power Rating

This is the most important factor to consider before choosing the gauge extension cord. There is a term “amperage” that is a unit for measurement. You will find 10,12-,14- and 16-gauge wires. Each wire used for a specific purpose. The 16 gauge is used for fans, lawnmowers, stereos, small appliances, and household tools. The 14-gauge used for heavy tools and machines such as drillers, routers, etc. 12 and 10 gauge used for more heavy usages, including generators, grinders, compressors, and many other heavy appliances and tools. So, one thing is clear: the fewer gauges, the more it can handle. Thick wires are more powerful.

2. Multi-outlets

Multiple outlets seem attractive but are not useful. You should ignore such fancy multiple-outlet wires if you are looking for a durable wire. The current and usage will get scattered, and you will not get the desired output. Overloading can happen at any time.

3. Usage

The wires are divided based on the usage too. Each wire is given a designation to define its working and usability. ‘S’ denotes general-purpose flexible wire. ‘V’ is for softer and more flexible vacuum wire. ‘W’ is for outdoor use. ‘P’ is used mainly with air conditioners indicating a parallel wire construction. ‘O’ is for oil resistance. And a few others too. You can easily look at the designation and select one for yourself.

4. Extension Cord Lengths

In most cases, the cord’s power capacity is determined in terms of its length. Longer extension cords have higher resistance to the current, and it causes regular voltage drops. To get the best results, it’s better to use the shortest extension cord to run devices with high current requirements.

Extension Cord Gauge Chart (Amperage)

Check out the below usage and amp rating chart of different extension cord sizes, to know what size suits your requirement.

GaugeUsage25 Ft50 Ft100 Ft
16 Gauge U-GroundMedium Duty13 Amps13 Amps10 Amps
14 Gauge U-GroundHeavy Duty15 Amps15 Amps13 Amps
12 Gauge U-GroundExtra Heavy Duty15 Amps15 Amps15 Amps
12 Gauge TwistlockExtra Heavy Duty20 Amps20 Amps15 Amps
10 Gauge U-GroundUltra Heavy Duty15 Amps15 Amps15 Amps
10 Gauge TwistlockUltra Heavy Duty20 Amps20 Amps20 Amps

How to tell Gauge of Extension Cord?

You can tell the gauge of extension cords in different ways. One is by simply checking the cord. On the extension cord itself there will be printed numbers and letters like; 12/3, which means 12-gauge with 3 wires or 16AWG, which means 16-gauge or AWG16x2C, means 16-guage with 2 wires. Else, you can check the box or use the thickness of your cord to determine the gauge.

Types of Extension Cords

  • Plug-type: Most of the extension cords are either 2 prongs or 3. The 2 prong plug is not grounded while the 3 prong plug is by default. The purpose of a grounded prong is to reduce the risk of electrical failure or heat emission at times.
  • Cord thickness: Measuring a cord thickness is usually done in gauge or AWG. The higher the number of gauges, the lower is its power. In general households and daily usage equipment, 16 to 14 gauge is used. Lower gauge cords used for high-power devices and heavy usage.
  • Amperage: Amperage ratings are another factor to consider while buying the cord. It is all about the current capacity a wire can handle. Extension cords designed for handling a certain amount of current only. Before buying a cord, you can always check the current a device can handle. 
  • Indoor: Indoor wires come with both 2 and 3 prong plugs. Lengths vary from 3 to 15 meters. Indoor purposes include using fans, lamps, or any other electrical appliances. Generally, we use 16 or 14 gauge wires.
  • Outdoor: Outdoor wires are coated for outdoor purposes only and are weather resistant. These are long and flexible. You will see these cords connected to a generator or any outdoor appliance.
  • Contractor Purpose: Cords used specifically for Jobsite areas are contractor graded. They are designed to resist almost every weather condition. You will see such wires in a shop or any working garage. These wires are ‘O’ graded, which means they are oil resistant too.

Do’s and Don’ts of Gauge Extension Cord

Wires and cords vary from amperage ratings to power and thickness. Since we are buying an electrical cord, we should keep certain tips in mind. Keep the following things in your mind

Selection of Wire

  • Be aware of the usage and the environment you want to use it in.
  • Purchase certified rating wires only.
  • Consider the length; if in doubt, always buy the one bigger in length.
  • Buy an outdoor wire if you consider using it in an outdoor location.

Using Cords

  • There are 2 prongs and a 3 prong plug. 3 prongs come with a ground extension.
  • Do not use multiple devices with a low amperage wire. This would cause an electric failure.
  • Do not overuse the wire if it is heating.
  • Try not to bend or wrap the wire.

Always store wires indoors and do not heat them at any cost. Unplug the cords when not in use. Do not use the damaged cords and never pull the wires; always pull from the plug.


You should always take precautions while using an extension wire. Extension wires lead to overheating and failures if multiple devices are connected. This is due to overloading. Take extra precautions for preventing shocks and heating issues. Hope with this extension cord gauge guide, you are now clear about which extension cord you should pick. However, consider going through it for buying the perfect gauge and best extension cord that fits your requirement.

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