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How to Choose an Extension Cord (Gauge & Length)
The wrong extension cord doesn’t just underperform — it can overheat, starve your tool of power, or start a fire inside the wall of insulation you coiled it against. The right one is boring: it just works, cool to the touch, for years. Picking it comes down to two numbers.
The short answer
Match the cord to the load and the distance. For most homeowners, a 12-gauge (12 AWG), 50-foot outdoor-rated cord handles nearly anything — power tools, mowers, pressure washers — with room to spare. Lower gauge numbers mean thicker wire and more capacity. The longer the run and the hungrier the tool, the thicker the cord you need. Indoors and light-duty? A 16-gauge cord is fine. Never coil a cord under load, and always use an outdoor-rated (“W”) cord outside.
Gauge is the number that actually matters
Wire gauge (AWG, American Wire Gauge) describes how thick the copper conductors are inside the cord. Here’s the counterintuitive part: smaller numbers mean thicker wire. A 10-gauge cord is heavier and carries more current than a 16-gauge cord. Thicker wire has less resistance, so it delivers more of the outlet’s voltage to your tool and wastes less as heat.
That heat is the whole ballgame. Undersized cords drop voltage over distance, which makes motors run hotter, work harder, and die younger. A saw that bogs down or a drill that feels gutless on a long cord usually isn’t weak — it’s starving. Southwire and other quality makers stamp the gauge and length right on the jacket; if you can’t read it, don’t trust it.
Length works against you
Every foot of cord adds resistance and drops a little more voltage. That’s why a 25-foot cord and a 100-foot cord in the same gauge are not interchangeable. Run 100 feet of thin 16-gauge to a circular saw and you may lose enough voltage to trip the tool or cook the motor over time.
The fix is simple: as the run gets longer, step the wire thicker. Buy the length you actually need — don’t solve a 30-foot problem with a 100-foot cord and coil the extra, because a coiled cord under load traps heat like a heating element. If you routinely need reach, own two lengths rather than one long one.
The gauge-and-length chart
This is the cheat sheet. Find your tool’s amp draw (it’s on the nameplate or in the manual), then read across to the length you need. When you’re between sizes, go thicker — a heavier cord is never the wrong call.
| Tool load (amps) | Up to 25 ft | Up to 50 ft | Up to 100 ft |
|---|---|---|---|
| 1–7 A (lamps, chargers, small tools) | 16 AWG | 16 AWG | 14 AWG |
| 7–10 A (drills, sanders, string trimmers) | 16 AWG | 14 AWG | 12 AWG |
| 10–13 A (circular saws, mowers, pressure washers) | 14 AWG | 12 AWG | 10 AWG |
| 13–15 A (heaters, large saws, shop vacs) | 12 AWG | 12 AWG | 10 AWG |
Tip: a 15-amp space heater on a thin cord is one of the most common household fire causes. Space heaters should run on a heavy 12- or 14-gauge cord kept short — or better, plugged straight into the wall.
Indoor, outdoor, and the letters on the jacket
The jacket rating tells you where a cord is allowed to live. Outdoor cords carry a “W” and use tougher, UV- and moisture-resistant insulation (SJTW, SJOW). Indoor-only cords (SPT, SJT) crack and fail when the sun and cold get at them. Using an indoor cord outside is a genuine shock and fire hazard, not a technicality.
- SJTW / SJOW – outdoor-rated, all-weather — the default for yards, driveways, and jobsites.
- Three-prong (grounded) – required for any power tool or anything with a metal body. Never cut the ground pin off.
- Amp/wattage rating – printed on the tag; the cord must be rated for at least as many amps as everything plugged into it combined.
- Lighted end – a glowing plug tells you at a glance the cord is live — handy on jobsites and around portable work lighting.
For anything outdoors, protect the run with a GFCI — either a GFCI-protected outlet or an inline GFCI adapter on the cord. Water and electricity is exactly the scenario ground-fault protection exists for, whether you’re running a pressure washer or holiday lights.
Cords vs. power strips vs. surge protectors
These get used interchangeably and shouldn’t be. An extension cord moves power to a spot. A power strip splits one outlet into several. A surge protector adds circuitry that clamps voltage spikes to shield electronics. Daisy-chaining a power strip off an extension cord off another strip is how you overload a circuit — pick the right tool instead of stacking them.
For a desk, entertainment center, or anything with a circuit board, choose a real surge protector from the power strips and outlet devices aisle, not a bare cord. For delivering power to a tool across the garage or yard, that’s a job for a proper extension cord.
Pick by the job
AROUND THE HOUSE
Lamps, phone chargers, a fan on the porch. A 16-gauge, 25- to 50-foot cord is plenty. Grounded and outdoor-rated if it ever leaves the living room.
YARD & GARAGE
Mowers, trimmers, drills, a shop vac. Go 14- or 12-gauge, 50 to 100 feet, SJTW outdoor jacket. The one cord that covers most weekend projects.
HEAVY & FAR
Table saws, pressure washers, welders, or a generator feed. 12- or 10-gauge, kept as short as the run allows. Check the tool’s amp draw first, then go thicker.
Shop the whole project
Get powered up the right way
Every cord and connector we carry comes through authorized manufacturer channels — the trusted brands your neighborhood hardware store stands behind. See our guarantee.
Frequently asked questions
What gauge extension cord do I need?
Match gauge to the tool’s amp draw and the length of the run. For most homeowner tasks up to 50 feet, a 14- or 12-gauge cord is ideal. Light-duty items under 50 feet can use 16-gauge. Longer runs or higher amp draws need thicker wire — when in doubt, go one gauge heavier.
Is a lower gauge number thicker or thinner?
Lower numbers mean thicker wire. A 10-gauge cord is much heavier and carries far more current than a 16-gauge cord. Thicker wire has less resistance, so it delivers more power and runs cooler under load.
Can I use an indoor extension cord outside?
No. Outdoor cords are marked with a “W” and use UV- and moisture-resistant insulation like SJTW. Indoor-only cords crack and fail when exposed to sun, cold, and water, creating a real shock and fire risk. Always use an outdoor-rated, grounded three-prong cord outside.
Why does my extension cord get warm?
A cord warms up when it’s carrying more current than its gauge is rated for, or when it’s coiled while under load and trapping heat. If a cord feels hot, unplug it, uncoil it fully, and switch to a thicker gauge for that tool. A properly sized cord stays cool to the touch.
Can I plug a space heater into an extension cord?
It’s best to plug space heaters directly into a wall outlet. If you must use a cord, use a heavy 12- or 14-gauge cord kept as short as possible, and never a thin household cord or a power strip. Undersized cords on high-wattage heaters are a leading cause of home fires.
Buy the gauge your longest, hungriest tool needs and you’ll never think about it again. Not sure what your project draws? Bring the tool’s amp rating to your local independent hardware store and someone will hand you the right cord in thirty seconds — or ask us here and we’ll point you to it.
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