Cord guide

How to choose an extension cord: length, gauge and where it runs

A cord is rated for its length and its wire. Here is how to pick one that stays cool.

An extension cord is rated for two things at once: the thickness of its wire and its length. The same 16-gauge wire that carries 13 A over 50 ft carries only 10 A over 100 ft, because a longer run warms up more under the same current. Get those two right and the rest follows.

Length and gauge

Wire gauge (AWG) counts down as the wire gets thicker, so 14 AWG is heavier than 16 AWG. The Electrical Safety Foundation publishes this table of the current each gauge can carry at each length:

Cord length	Gauge	Up to
25 to 50 ft	16 AWG	13 A
25 to 50 ft	14 AWG	15 A
100 ft	16 AWG	10 A
100 ft	14 AWG	13 A
100 ft	12 AWG	15 A

That is why our 16 AWG outdoor cord is rated 13 A in its short lengths and 10 A at 100 ft, and why the long surge strips and power stakes use 14 AWG. To pick a length, measure the route the cord will follow along the ground or the wall, not the straight line, add a couple of feet, and take the next length up.

Indoors or outdoors

Use a cord marked for outdoor use outside. The U.S. Consumer Product Safety Commission lists a jacket over the wires as a required feature of outdoor cords, and OSHA asks for 3-wire grounded cords. Our indoor/outdoor cords are 3-prong, 16 AWG, from 3 to 100 ft. The 2-prong cords with safety shutters and the flat plug cords are for indoors only.

2-prong, 3-prong and flat plugs

A 2-prong polarized cord suits lamps and chargers with 2-prong plugs. Anything with a grounded 3-prong plug needs a 3-prong cord, and the Electrical Safety Foundation warns never to cut off the ground pin to make it fit. A flat plug lies against the wall, so furniture can stand close to the outlet.

Using a cord safely

Treat an extension cord as temporary. If you rely on one every day, the room needs another outlet.
Add up the watts of what you plug in and stay under the cord rating. Heaters and major appliances go straight into a wall outlet.
Do not run a cord under a rug, through a doorway or through a wall, where it cannot shed heat or gets pinched.
Do not chain one multi-outlet device into another. Pick a cord long enough instead.
Replace a cord that is cut, cracked or feels hot.

These points come from the Electrical Safety Foundation and the U.S. Fire Administration, listed below with the date we read them.

This is general safety information, not electrical advice for your home. The rating printed on the device and the instruction sheet in the box are the final word, and wiring questions belong with a licensed electrician.

What the safety sources say

Electrical Safety Foundation International, Extension Cord Safety Tips. Treats an extension cord as a temporary fix, asks you to match the cord rating to the wattage of what you plug in and to use a cord marked for outdoor use outside, and lists amperage limits by length: a 100-foot 16-gauge cord is good for up to 10 amps, a 25 to 50-foot one for up to 13. Read September 28, 2026.
U.S. Consumer Product Safety Commission, Extension Cords. Lists the features every household extension cord must show under UL 817: minimum wire size, strain relief, polarity and continuity, outlet covers on indoor cords and a jacket on outdoor cords. Read September 28, 2026.
Occupational Safety and Health Administration, Flexible Cords. Explains that cords are damaged by door and window edges, staples and age, and that a wet connector can leak current, so connectors should be kept out of standing moisture. Read September 28, 2026.
U.S. Fire Administration, Appliance and Electrical Fire Safety. Advises not to overload power strips, to pick strips with internal overload protection, to keep cords out from under rugs and to replace worn or damaged cords right away. Read September 28, 2026.

Our sources and how we keep this catalog

Surge protector strip