Extension Cord Gauge Calculator
Find the right extension-cord wire gauge (AWG) for a device from its wattage or amps and the length of cord you need to run.
How it works
Current (A) = watts ÷ volts · Gauge chosen from a length × current chart (thicker wire for longer runs and higher current)
A long cord acts like a small resistor: the further electricity travels, the more voltage it loses and the hotter a thin wire gets, so longer runs and bigger loads both demand thicker copper (a lower AWG number). Undersized cords sag the voltage, make motors and heaters run hot, and are a genuine fire risk. When in doubt, size up — a thicker cord never hurts and runs cooler.
Worked example
A 1,200 W heater on a 120 V supply draws 1,200 ÷ 120 = 10 A. Over a 50 ft run the chart calls for 16 AWG; if you extended it to 100 ft you would step up to 14 AWG to keep the voltage drop safe.
Sources: American wire gauge (Wikipedia)
Frequently asked questions
What does AWG mean, and is lower thicker?
AWG is American Wire Gauge. Counter-intuitively, a lower number means a thicker wire — 12 AWG is thicker and carries more current than 16 AWG. Thicker wire has less resistance, so it loses less voltage and stays cooler over long runs.
Why does cord length change the gauge I need?
Resistance is proportional to length, so a longer cord drops more voltage and heats up more for the same current. To keep the voltage drop and heating within safe limits, longer runs need thicker wire (a lower AWG) than short ones carrying the same load.
Can I daisy-chain two extension cords?
It is strongly discouraged. Joining cords adds length and resistance, increases voltage drop and creates extra connection points that can overheat. Use one correctly sized cord instead, or move the device closer to an outlet.
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This calculator is for educational purposes. Double-check important results before acting on them.