Extension Cord Gauge, Amperage and Length
When shopping for extension cords, you’ll notice four key measurements: gauge, amperage, wattage and length. Understanding these factors and how they relate will help you find the best extension cord for your device or appliance.
Extension Cord Gauge
Extension cord gauge indicates the thickness of the conducting wire. Lower numbers indicate thicker wire and higher numbers mean a thinner wire. In general, extension cords with lower gauge numbers can carry more current than comparable cords with higher gauge numbers.
Extension Cord Amperage
Amperage, indicated in amps, measures the maximum electrical current a cord can safely carry. The amp rating for a cord should be equal to or greater than those a device draws when in use.
Extension Cord Wattage
Wattage measures the amount of energy the cord can safely carry. As with amps, an extension cord needs to be able to deliver a number of watts equal to or greater than the device it’s powering.
Extension Cord Length
Length is a critical factor in the current and electricity the cord can carry. Longer cords create more electrical resistance and can’t carry the same amount of amperage and wattage as a shorter cord of the same gauge. A 100-foot extension cord, for example, will need to have a lower gauge number to safely deliver the same amount of current and energy as a 25-foot extension cord.
Extension Cord Types
While it seems like a basic factor, one of the first choices you need to make when purchasing an extension cord is between an indoor extension cord and an outdoor extension cord. Knowing how they compare will help you choose the right option.
Indoor Extension Cords
Indoor extension cords are typically between 6 and 15 feet long, though you can find them in many lengths. Since indoor devices often don’t draw high amps, these are usually light- to medium-duty extension cords with wire gauges between 18 and 14 and less insulation than an outdoor cord. You can find grounded — three-prong plugs — and ungrounded — two-prong plugs — indoor extension cords. Indoor cords aren’t suitable for exposure to sunlight, moisture and wide temperature changes.
Look for indoor extension cords with space-saving flat plugs that fit closely against the wall behind furniture, televisions, etc. You can also find indoor cords with decorative jackets to blend with your décor.
Outdoor Extension Cords
Outdoor extension cords have thicker insulation that can resist moisture, temperature variations and ultraviolet rays from sunlight. Some may have insulation or jacketing that keeps them flexible when temperatures drop below freezing. Outdoor extension cords are commonly available in lengths of 25, 50 and 100 feet, with low gauges, usually 16 to 10, and amp ratings from 10 to 30 or more. Outdoor extension cords are grounded cords with three-prong plugs that include the grounding pin. The plug and connector ends may be lighted for visual confirmation that the cord has power.
You can find outdoor extension cords in bright orange, yellow, pink or green to make them highly visible on work sites or in dark green and black to help them blend into your landscape when powering outdoor holiday décor.
Indoor/Outdoor Extension Cords
Some cords are suitable for use either inside or outside of the home. Indoor/outdoor extension cords are typically 10, 25, 50 or 100 feet in length. Wire gauge numbers are in the middle range, typically from 14 to 10. Amp ratings usually run from 10 to 30.
When shopping for a corded power tool or a corded piece of outdoor landscape equipment, remember to factor the cost of a suitable extension cord into your purchase. A tool or piece of equipment that draws a high level of amps will require a heavy-duty, low-gauge outdoor power cord in a length that’s practical.
Extension Cord Gauge Guides and Usage Tips
The best and safest way to match an extension cord to a tool, appliance or other device is to check the wattage and amperage requirements of the device and purchase an extension cord with capabilities that exceed those requirements. We’ve got some general tips for selecting extension cords for different uses, but always rely on the device manual and cord information.
Follow the device and cord manufacturer specifications for extension cord ratings and use. Some tools, equipment, appliances and devices have specific requirements for cord gauges and amp ratings.
While some longer cords may be capable of carrying a particular amp load, you may see a voltage drop that can reduce performance or damage the device. It’s best to go with the shortest cord that is practical.
25-Foot Extension Cords
Depending on the actual amp and wattage rating of the cord:
- A 25-foot, 16-gauge cord can work for hedge trimmers or jigsaws that draw up to 12 amps.
- A 25-foot, 14-gauge cord can work with mowers and power tools that draw 12 to 15 amps.
- A 25-foot, 12-gauge cord can work with circular saws and table saws that draw 15 to 20 amps.
- A 25-foot, 10-gauge cord can work with tools that draw 15 to 20 amps.
50-Foot Extension Cords
Depending on the actual amp and wattage rating of the cord:
- A 50-foot, 16-gauge cord can work with space heaters or jigsaws that draw up to 12 amps.
- A 50-foot, 14-gauge cord can work with drills or sanders that draw 12 to 15 amps.
- A 50-foot, 12-gauge cord can work with circular saws and grinders that draw 15 to 20 amps.
- A 50-foot, 10-gauge cord can work with hammer drills, circular saws and industrial machines that draw 15 to 20 amps.
100-Foot Extension Cord
Depending on the actual amp and wattage rating of the cord:
- A 100-foot, 16-gauge cord can work with fans and basic power tools that draw up to 6 amps.
- A 100-foot, 14-gauge cord can work with routers or sanders that draw 6 to 12 amps.
- A 100-foot, 12-gauge cord can work with grinders or table saws that draw 12 to 15 amps.
- A 100-foot, 10-gauge cord can work with compressors and power saws that draw 15 to 20 amps.
Extension Cords for Appliances
You’ll see some extension cords designated as appliance extension cords. Extension cords for appliances tend to be heavy duty, low-gauge cords rated for 15 to 40 amps. They will have thick insulation and may have a plug configuration to match dedicated electrical receptacles for appliances such as dryers. Some can also work with welders and electric vehicle (EV) charging systems.
Extension Cords for Generators
Generator extension cords connect your electrical devices to a portable generator. Generator cords tend to be heavily insulated, low-gauge — 10 gauge to 6 gauge — cords that are rated for 30 to 50 amps. Some have a plug configuration specific to a high-amp receptacle on a generator. Extension cords for RVs (recreational vehicles) will have similar designs.
Extension Cord Safety
Safely using an extension cord first requires you to match the cord ratings to the tool, or device specifications. While the information above gives you a general idea of which cords work with which devices, you must always check the device manual or specifications to find a suitable extension cord or to confirm you can use an extension cord. We have a few safety tips below, but always follow the cord and device specifications and safety instructions.
- Use the right cord type. Use indoor extension cords indoors. If you need an extension cord to power something outdoors, use an outdoor-rated cord.
- Pay attention to the plug type. If your tool or device has a 3-prong grounded plug, use a grounded extension cord. If the device plug is a 2-prong ungrounded plug, you can use either a grounded or ungrounded extension cord.
- Don’t exceed the wattage or amp rating of an extension cord. A device that draws more amperage than the cord can carry risks overheating, leading to damage of the cord and potentially, a fire. Mismatching the cord and device can also mean your device doesn’t get the power it needs, leading to poor performance and even damage to the device.
- If you notice an extension cord is hot, stop using it and unplug it.
- Don’t overload an extension cord. Don’t attach more than one device unless the cord is designed to accept multiple devices. Keep in mind all of the attached equipment that will be operating at the same time and make sure the cord and the power receptacle are rated to handle the load of all of the devices.
- Don’t use a damaged cord. Inspect an extension cord before using it. Damage to the plug, connector, wires or insulation creates a risk of fire, shock and burns.
- Use GFCI (ground-fault circuit interrupter) receptacles for extension cords when working in an area where moisture or water is a concern. Use them when working outdoors as well as when working in bathrooms, kitchens, garages, basements, crawl spaces, etc. Some outdoor extension cords have built-in GFCI protection.
- Be aware of tripping hazards extension cords can create. Keep them out of walkways as much as possible and make sure they’re easily visible and secure.
- Don’t cover an extension cord with a rug, tarp, etc. Covering a cord can lead to overheating.
- Don’t connect multiple extension cords together. Use a single, longer extension cord instead.
Learning how to wrap an extension cord can reduce the risk of damage. See our guide Wrapping Extension Cords for three techniques you can try. Extension cord reels can also make storing extension cords and organizing extension cords easier.