Extension Cord Gauge Calculator
Enter your appliance wattage and cord length to find the minimum safe AWG gauge, and avoid overheating, voltage drop, and fire risk.
Find the right extension cord gauge
Enter your device load and the cord length you need.
12 AWG minimum
For a 1,500W device at 120V over 25 feet.
How to use this calculator
Enter the wattage of the device you need to power (from the label or manual), select the circuit voltage (almost always 120V for standard US outlets), and enter the cord length in feet. The calculator converts wattage to amperage, then determines the minimum AWG gauge needed to safely carry that current over that distance without dangerous voltage drop or heat buildup.
Tips for success
- AWG works backwards, a lower number means a thicker, heavier wire with more capacity. Never substitute a lighter gauge when a heavier one is called for.
- Motors (refrigerators, pumps, air compressors) draw 2–6× their running watts at startup. Size the cord using surge wattage for any motorized appliance.
- Never use indoor-only cords outdoors, outdoor cords are UV-, moisture-, and temperature-rated. An indoor cord outdoors is a fire and shock hazard.
- Never run cords under rugs, through walls, or in concealed spaces. Heat buildup in enclosed areas is a leading cause of extension-cord fires.
- For generators, use a cord rated for the generator's output amperage, undersized cords can melt under sustained load even when small appliances would be fine.
AWG gauge quick reference
- 16 AWG: Light loads up to 13A (1,560W at 120V). Good for lamps, fans, phone chargers, small electronics over short distances (25 ft or less).
- 14 AWG: Medium loads up to 15A (1,800W at 120V). Suitable for most portable heaters, window AC units, power tools, and kitchen appliances up to 50 ft.
- 12 AWG: Heavier loads up to 20A (2,400W at 120V). Required for refrigerators, larger AC units, circular saws, and generators. Safe up to 100 ft.
- 10 AWG: Heavy loads up to 30A (3,600W at 120V). Used for large generators, RV hookups, welders, and high-demand power tools. Essential for runs over 100 ft with heavy loads.
FAQ
What happens if I use a gauge that's too light?
An undersized extension cord acts like a resistor, the wire heats up as current flows through it. At low excess, you'll see voltage drop (equipment runs slower or dims). At higher excess, the insulation melts, which can cause a fire. The cord may not trip a circuit breaker because breakers protect circuits, not the cord itself.
Can I daisy-chain extension cords together?
Technically yes, but it's generally not recommended and is against electrical code for permanent use. Each connection adds resistance and potential failure points. If you need length, buy a single long cord of the appropriate gauge. Never connect two cords of different gauges, the lighter gauge determines the safe capacity of the entire run.
Why does cord length affect the gauge I need?
Electrical resistance increases with wire length. A longer cord has more resistance, which causes more voltage to be "used up" in the cord rather than reaching the appliance. A heavier gauge has lower resistance per foot, which compensates for longer runs and keeps voltage drop within safe limits (typically under 5%).
What cord gauge do I need for a portable generator?
Most portable generators output 20–30 amps. A 10 AWG cord is appropriate for loads up to 30A and runs up to 100 ft. Look for cords specifically labeled "generator cord" or "heavy-duty outdoor" with a matching amperage rating. The plug style (NEMA 5-15, 5-20, L5-30, etc.) must match your generator's outlet.