Extension cord gauge calculator
A cord that’s too thin for its length overheats and starves tools of power. Enter what you’re plugging in and how long a cord you need.
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
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How it works
Two things decide the gauge. First, the cord has to carry the current safely. Typical ratings are 10 amps for 18 gauge, 13 for 16 gauge, 15 for 14 gauge and 20 for 12 gauge. Second, long thin wires lose voltage, which makes motors run hot and lights dim. The calculator works out the voltage drop from the copper wire’s resistance over the cord’s length there and back, and picks the thinnest cord that keeps it under 5%.
Lower gauge numbers are thicker wire: 12 gauge is heavier than 16.
Example
With power draw 1,200 watts, cord length 100 ft, the answer is 14 gauge (AWG).
Tips before you buy
- When in doubt, go one size heavier. A thicker cord costs a little more and never hurts.
- Outdoors, use a cord marked for outdoor use (a “W” on the jacket), and keep connections off wet ground.
- Don’t use extension cords for space heaters. Plug heaters straight into a wall outlet.
- A cord that feels warm is overloaded. Unplug it and use a heavier gauge or a shorter run.
Common questions
What gauge extension cord do I need for 100 feet?
For a 10 amp tool, 14 gauge. For 13 amps, 12 gauge. For a small load under 5 amps, 16 gauge is fine.
What gauge extension cord for Christmas lights?
LED light displays draw little power. A 16 gauge outdoor cord handles up to 13 amps (about 1,560 watts) at 50 feet.
Is 12 gauge thicker than 14 gauge?
Yes. The smaller the gauge number, the thicker the wire and the more current it can carry over a longer distance.