🔌 Extension Cord Gauge Calculator
A smaller AWG number = thicker wire = handles more current safely. Never use a cord that's too thin.
Extension Cord AWG Gauge Reference Chart
Use this table as a quick reference. For heavy loads or long runs, always step up (lower number) one gauge for safety margin.
| AWG Gauge | Max Amperage | Max Watts (120V) | Max Cord Length | Common Use |
|---|---|---|---|---|
| 16 AWG | 13A | 1,560W | 25 ft | Lamps, small electronics, phone chargers |
| 14 AWG | 15A | 1,800W | 50 ft | Refrigerators, fans, small appliances |
| 12 AWG | 20A | 2,400W | 100 ft | Power tools, space heaters, window A/C units |
| 10 AWG | 30A | 3,600W | 100 ft | Large loads, generator to transfer switch |
| 8 AWG | 40A | 4,800W | 50 ft | Heavy-duty generator power cords |
Ampacity values reflect continuous-duty derating per NEC guidelines (80% of wire capacity). Actual extension cord ratings may vary by manufacturer.
Why Extension Cord Gauge Matters for Generators
The most common and dangerous mistake when connecting a generator is using an undersized extension cord. An undersized cord does two things:
- Overheats and potentially catches fire. Resistance in a thin wire causes heat proportional to current². A 16 AWG cord carrying 15A (the load of a small space heater) will exceed safe operating temperature. The cord jacket melts or ignites, especially if coiled.
- Causes voltage drop. Resistance in a long, thin wire reduces voltage at the far end. Sensitive electronics and motors receive lower-than-rated voltage, causing overheating, reduced output, and premature failure. A motor receiving 102V instead of 120V draws extra current to compensate — worsening the problem.
The Two Variables: Amperage and Length
AWG selection is determined by two factors working together. Amperage determines the minimum gauge; length determines whether you must step up to the next heavier gauge:
- Amperage (I = P / V): A 1,440W load on 120V draws 12A. A 14 AWG cord (rated 15A continuous) is borderline adequate on a 25 ft cord but insufficient at 100 ft.
- Length: Every foot of wire has resistance. At 50 ft a 14 AWG carries 1,440W safely; at 100 ft you need 12 AWG for the same load due to cumulative voltage drop.
Never use a coiled extension cord under load. A coiled 50 ft cord acts like a resistor and generates significant heat. Always unroll completely before use.
Generator-Specific Cords
Most portable generators include a twist-lock 30A NEMA L14-30 outlet (for 4-prong, 240V, 30A connections). If you're using a generator-to-transfer-switch cable or a heavy-duty multi-outlet "spider" cord, ensure it is rated for your generator's full output, not just the load you plan to draw. Using a 10 AWG cord (30A rating) is the minimum for connecting a 7,500W generator at any cord length under 100 ft.
Frequently Asked Questions
For most generator connections, you need at least 12 AWG. Generators that supply 30A circuits require a 10 AWG cord minimum. Never use 16 AWG for generator connections — the amperage draw from typical loads will exceed its safe capacity, causing the cord to overheat. Use the calculator above for your specific wattage and cord length.
Yes, but you must step up to a heavier gauge. A 100 ft cord at a typical load (1,400–2,000W) requires 12 AWG — one gauge heavier than a 25 ft cord for the same appliance. For loads above 2,400W at 100 ft, use 10 AWG. Beyond 100 ft, consider whether you can move the generator closer rather than going to an extremely long run.
AWG (American Wire Gauge) works backwards — a lower number means a thicker, heavier wire: 10 AWG is thicker than 12 AWG, which is thicker than 14 AWG. Thicker wire carries more current safely and loses less voltage over distance. For generator use: 16 AWG is acceptable only for very light loads (lamps, phone chargers) on short runs. 14 AWG is for small appliances 25 ft or less. 12 AWG covers most household appliances up to 100 ft. 10 AWG covers heavy loads and generator power cords.
The "W" suffix in an extension cord's model or jacket marking means it's rated for outdoor wet locations. Cords without this rating must only be used indoors on dry surfaces. For generator use (which always requires outdoor operation), you must use a cord with a "W" outdoor rating. Look for cords marked SJTW or STOW on the jacket to confirm outdoor suitability.