What gauge extension cord do I need?
Short answer
For a tool drawing up to 15 amps (1,800 watts), use 14 gauge up to 50 feet and 12 gauge at 100 feet. Light loads like LED Christmas lights are fine on 16 or 18 gauge. The smaller the gauge number, the thicker the wire.
Work it out for your numbers
Use a cord of at least
14 gauge (AWG)
- Current draw
- 10 amps
- Voltage drop with this cord
- 4.2 %
- With 16 gauge instead
- 6.7% drop
Gauge by load and length
| Load | 25 ft | 50 ft | 100 ft |
|---|---|---|---|
| 300 W (2.5 amps): LED light displays | 18 | 18 | 18 |
| 600 W (5 amps): small tools | 18 | 18 | 16 |
| 1,200 W (10 amps): drills, sanders | 18 | 16 | 14 |
| 1,500 W (12.5 amps): saws, shop vacs | 16 | 16 | 12 |
| 1,800 W (15 amps): biggest plug-in tools | 14 | 14 | 12 |
Minimum gauge to carry the current safely and keep voltage drop under 5%. Going thicker is always fine.
Two things decide the gauge
Current. Amps = watts ÷ 120. Typical cord ratings are 10 amps for 18 gauge, 13 for 16 gauge, 15 for 14 gauge and 20 for 12 gauge. Too much current overheats the cord.
Length. Long thin wires lose voltage, so motors run hot and lights dim. That’s why the same 1,500 watt saw is fine on 16 gauge at 50 feet but needs 12 gauge at 100.
Safety
- Don’t run space heaters on extension cords. Plug them straight into the wall.
- Outside, use cords marked for outdoor use (look for a “W” in the jacket code, such as SJTW).
- Uncoil a cord fully before running a heavy load through it. A coiled cord can’t shed heat.
- Don’t chain cords together to reach farther. Buy one cord the right length.
Common questions
What gauge extension cord for 100 feet?
12 gauge for tools drawing 12.5 to 15 amps, 14 gauge for about 10 amps, and 16 gauge for light loads around 5 amps.
Is 16 gauge OK for Christmas lights?
Yes, for typical LED displays. Even 18 gauge handles a few hundred watts at 100 feet.
Is a lower gauge thicker?
Yes. 12 gauge is thicker and carries more current than 16 gauge.
Updated October 29, 2026. Figures are estimates for planning. Check product labels and local codes before you buy or build.