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Pick the right portable extension cord gauge based on your tool's amp draw and the length of the cord. Because voltage drops over distance, longer cords need thicker wire to safely run power tools without overheating or underperforming.
The right extension cord gauge depends on both the tool's amp draw and the cord length, because voltage drops over distance. As a rule of thumb: for up to a 25 ft cord use 16 AWG for light loads or 14 AWG for power tools; for 50 ft use 14 AWG (or 12 AWG for heavy tools); for 100 ft use 12 AWG, stepping up to 10 AWG for high-amp tools like table saws and compressors. Remember: lower gauge number = thicker wire = more capacity. See the full length-and-amp chart below.
12/3 SJTW outdoor cord rated for 15A. The go-to size for power tools at 50 feet — handles circular saws, miter saws, and shop vacs.
View on Amazon10/3 SJTW heavy-duty cord for high-amp tools at long distances. Best choice for table saws and air compressors at 100 feet.
View on Amazon14/3 contractor-grade cord for light to medium power tools on shorter runs. Flexible and easy to coil for jobsite use.
View on AmazonCord with a lighted female end so you can see at a glance that it has power. Handy in dim shops, garages, and outdoors.
View on AmazonRetractable or hand-crank reel to keep long cords tangle-free and stored neatly. Look for 12 AWG reels for power tool use.
View on AmazonAs an Amazon Associate, WorkshopCalc earns from qualifying purchases.
Find your tool's amp draw in the left column, then read across to your cord length to get the recommended minimum wire gauge (AWG). These values follow widely-published outdoor and power-tool cord recommendations and are rounded up to the thicker wire when in doubt. Remember: a lower gauge number means a thicker wire.
| Amp Load | 25 ft | 50 ft | 100 ft | 150 ft |
|---|---|---|---|---|
| 1-2 A | 18 AWG | 18 AWG | 16 AWG | 14 AWG |
| 3-5 A | 16 AWG | 16 AWG | 14 AWG | 12 AWG |
| 6-8 A | 16 AWG | 16 AWG | 14 AWG | 12 AWG |
| 9-10 A | 14 AWG | 14 AWG | 12 AWG | 10 AWG |
| 11-13 A | 14 AWG | 14 AWG | 12 AWG | 10 AWG |
| 14-15 A | 14 AWG | 12 AWG | 10 AWG | 8 AWG |
| 16-20 A | 12 AWG | 10 AWG | 8 AWG | 8 AWG |
Recommended minimum gauge for portable extension cords. Values are conservative (rounded up to thicker wire) to keep voltage drop low enough for proper motor operation. When in doubt, go thicker.
Not sure which amp row applies to your tool? Use this table to find a typical amp draw, then match it to the chart above. Check your tool's nameplate or manual for its exact rating, since amps vary by model.
| Tool / Device | Typical Amp Draw |
|---|---|
| LED light / battery charger | 1-2 A |
| Jigsaw / orbital sander | 4-6 A |
| Router | 8-12 A |
| Shop vacuum | 8-12 A |
| Air compressor | 10-15 A |
| Space heater | 12.5 A |
| Circular saw | 12-15 A |
| Miter saw | 13-15 A |
| Table saw (115V) | 13-15 A |
Startup (inrush) current on motor-driven tools can briefly spike well above the running amps listed here, which is another reason to size cords generously.
This is the approximate maximum current each cord gauge can carry on a short run. Capacity drops as the cord gets longer because of voltage drop, so always cross-check the length-and-amp chart above rather than relying on these maximums alone.
| Cord Gauge | Approx. Capacity | Notes |
|---|---|---|
| 16 AWG | ~13 A | Light-duty, short runs only |
| 14 AWG | ~15 A | Medium-duty power tools |
| 12 AWG | ~20 A | Heavy-duty / most shop tools |
| 10 AWG | ~30 A | Extra heavy-duty / long runs |
Caveat: these capacities apply to short cords. The longer the cord, the lower the usable capacity — a 100 ft cord effectively carries less than the same gauge at 25 ft.
Every foot of wire has a small amount of electrical resistance, and that resistance causes the voltage to drop along the length of the cord. The longer and thinner the cord, the more voltage is lost before it reaches your tool. This is why two identical cords of different lengths can behave completely differently.
When a motor receives less than its rated voltage, it tries to maintain power by drawing more current. That extra current generates heat in both the motor windings and the cord itself. The result is a motor that runs hot, bogs down under load, and may trip its overload protection — plus a cord that can become dangerously warm. Sizing up to a thicker (lower-gauge) wire reduces resistance, keeps voltage drop in check, and protects both your tool and the cord. As a target, keep voltage drop to about 5% or less for proper power-tool operation.
Extension cords are rated for where they can safely be used, and the jacket markings tell you which is which:
For any workshop, garage, or jobsite cord, choose an outdoor-rated SJTW cord even if you mostly use it indoors — the tougher jacket resists abrasion, oil, and moisture, and it's the safe default for power tools.
Extension cords are labeled with a simple gauge/conductor code printed on the jacket, such as 12/3. It breaks down like this:
So 12/3 = 12 AWG, 3 conductors. A three-conductor (grounded) cord is required for power tools with a three-prong plug. Common shop sizes include 14/3, 12/3, and 10/3 — the lower the first number, the heavier the cord. You may also see a gauge plus an amp or wattage rating elsewhere on the jacket.
It's tempting to plug one extension cord into another to reach farther, but daisy-chaining cords is a common cause of overheating and tool problems. Each connection adds resistance and another point of voltage drop, and the combined length quickly exceeds what the gauge can safely handle. Stacking a thin cord onto a thicker one means the whole run is only as strong as its weakest, thinnest section.
Instead of chaining, use a single cord that's long enough and properly gauged for the full distance, or move your power source closer to the work. If you regularly need long runs, invest in one heavy-gauge cord or a cord reel rather than linking several lighter cords together.
Calculating fixed wiring or a circuit instead of a portable cord? Use our wire size calculator for precise recommendations based on voltage, amperage, distance, and acceptable voltage drop.
Wire Size CalculatorA 115V table saw typically draws 13-15 amps, so use a 14 AWG cord for runs up to 25 feet, a 12 AWG cord for 50 feet, and a 10 AWG cord for 100 feet. For best performance, keep the cord as short as possible — long, thin cords cause voltage drop that makes the motor work harder and can trip the saw's overload protection. Whenever in doubt, choose the thicker (lower-number) gauge.
For a 100-foot extension cord, use 12 AWG for most power tools drawing up to about 13 amps, and step up to 10 AWG for high-amp tools like table saws, miter saws, and air compressors that pull 14-15 amps. Light loads such as lights or chargers under 8 amps can use 14 AWG at 100 feet. The longer the cord, the thicker the wire you need to offset voltage drop.
Yes. An undersized (too thin) extension cord causes excessive voltage drop, which starves the tool's motor of voltage. The motor then draws more current to compensate, overheating both the motor windings and the cord itself. Over time this can burn out motor windings, degrade tool performance, and create a fire hazard from the overheated cord. Always size the cord up for the tool's amp draw and the cord length.
On an extension cord, 12/3 means the cord uses 12 AWG wire and has 3 conductors (hot, neutral, and ground). The first number is the wire gauge — a lower number means thicker wire and more current capacity — and the second number is the number of conductors. A grounded cord with 3 conductors is required for power tools with three-prong plugs. So 14/3 is a 14-gauge, 3-conductor cord, while 10/3 is a heavier 10-gauge, 3-conductor cord.
For carrying current, yes — a lower gauge number means a thicker wire that can handle more amps with less voltage drop. A 10-gauge cord carries more current than a 12-gauge, which carries more than a 14-gauge. Thicker cords are heavier, stiffer, and cost more, so you don't always need the lowest gauge available. Match the gauge to your tool's amp draw and cord length: lower gauge for high-amp tools and long runs, higher gauge is fine for light loads on short cords.