What Gauge Extension Cord Do I Need? Length and Amps Chart
The gauge you need depends on the amps the tool draws and the length of the cord. A 14 gauge cord is good for a 13 amp saw up to 40 feet, and a 12 gauge cord for 70 feet, with a voltage drop of 3% or less. A lower gauge number means a thicker wire. If the cord is too thin or too long, the tool loses power, runs hot and wears out, and the cord can overheat. The voltage drop calculator checks any cord, and the watts to amps calculator turns a tool's watts into amps.
Longest cord by gauge and amps
The longest length (one way) for a voltage drop of 3% on a 120 volt cord:
| Cord | 5 A (drill, jigsaw) | 9 A (shop vacuum) | 13 A (circular saw) | 15 A (table saw) |
|---|---|---|---|---|
| 16 AWG | 70 ft | 35 ft | 25 ft | 20 ft |
| 14 AWG | 110 ft | 60 ft | 40 ft | 35 ft |
| 12 AWG | 180 ft | 100 ft | 70 ft | 60 ft |
| 10 AWG | 285 ft | 160 ft | 110 ft | 95 ft |
With a voltage drop of 5%, a limit some people accept for short use:
| Cord | 5 A (drill, jigsaw) | 9 A (shop vacuum) | 13 A (circular saw) | 15 A (table saw) |
|---|---|---|---|---|
| 16 AWG | 120 ft | 65 ft | 45 ft | 40 ft |
| 14 AWG | 190 ft | 105 ft | 70 ft | 60 ft |
| 12 AWG | 300 ft | 165 ft | 115 ft | 100 ft |
| 10 AWG | 480 ft | 265 ft | 185 ft | 160 ft |
Check the amps on the tool's label. Motors draw more when they start, so choose a gauge that is not at the limit, and keep a margin. For example, a 600 watt tool draws 5.0 amps at 120 volts.
What cord for what job
- Light duty (16 gauge): lamps, small fans and chargers, and short runs of up to 25 feet for small tools.
- Medium duty (14 gauge): drills, sanders and a shop vacuum, up to about 50 feet.
- Heavy duty (12 gauge): saws, pressure washers, compressors and heaters, and runs of 50 to 100 feet. A 12 gauge cord at 15 amps over 100 feet drops 4.9%.
- Very heavy duty (10 gauge): long runs to big tools, or a generator feeding a job site.
Safety and good habits
- Never exceed the amp rating on the cord. Typical ratings are about 13 amps for 16 gauge and 15 amps for 14 gauge, and up to 15 to 20 amps for 12 gauge, depending on the plug.
- Use a cord rated for outdoor use (marked W) outside, and plug it into a GFCI outlet.
- Uncoil a cord completely. A coiled cord under load gets hot.
- Do not run a cord under a rug or through a door, and replace one with cuts or bare wire.
- Do not use a cord as a permanent wire. If you need power in a place all the time, have an outlet installed.
- Plug heaters and air conditioners into the wall if you can, or use the heaviest short cord that you have.
For a longer-term circuit, see the wire size chart for 15 to 50 amps and the wire size calculator.
Frequently asked questions
What gauge extension cord do I need for a circular saw?
A saw draws about 13 to 15 amps. A 14 gauge cord is good for 40 feet, and a 12 gauge cord for 70 feet, with a voltage drop of 3% or less. Use 12 gauge for 50 feet or more.
What gauge cord for a 1500 watt space heater?
A 1,500 W heater draws 12.5 amps. Use a 12 gauge cord, kept short, and avoid an extension cord altogether if you can: plug heaters into the wall.
Does a longer extension cord need a thicker wire?
Yes. A longer cord has more resistance, so more voltage is lost along it and the cord gets warm. A lower gauge number is a thicker wire: 12 gauge is thicker than 16.
What does gauge mean on an extension cord?
The American wire gauge (AWG) of the conductors. The smaller the number, the thicker the wire and the more current it carries: 10, 12 and 14 gauge are heavy duty, and 16 and 18 gauge are light duty.
Can I plug two extension cords together?
It is better not to. Every joint adds resistance, and the total length counts for the voltage drop. Buy one cord of the right length and gauge.
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and follow local building codes for anything structural.