Extension Cord Calculator
Find the correct Wire Gauge (AWG) for your extension cord to prevent overheating, fire hazards, and ensure your tools get full power.
Load Details
Recommended Gauge
50 ft 12/3 Outdoor Waterproof Extension Cord
- Color: Yellow
- Brand: POWGRN
- Voltage: 125 volts of alternating current
- Plug Format: Type B
Essential Cord Gear
Professional equipment for safe power transmission.
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Cords
10/12 Gauge Cords
Minimize voltage drop with thick copper wiring. Essential for runs over 50ft or high loads.
Reels
Retractable Reels
Keep your workspace organized and cables tangle-free. Protects insulation from damage.
Inlets
Inlet Boxes (L14-30)
Safe outdoor connection point for connecting your portable generator to a transfer switch.
Adapters
Locking Adapters
Convert 240V locking outlets to standard 120V household plugs for multi-tool use.
Extension Cord Size Chart (120V)
| Cord Length | Up to 10 Amps | 11 - 13 Amps | 14 - 15 Amps | 16 - 20 Amps |
|---|---|---|---|---|
| 25 ft | 16 AWG | 16 AWG | 14 AWG | 12 AWG |
| 50 ft | 16 AWG | 14 AWG | 12 AWG | 10 AWG |
| 100 ft | 14 AWG | 12 AWG | 10 AWG | 8 AWG |
| 150 ft | 12 AWG | 10 AWG | 8 AWG | 6 AWG |
The Science Behind the Calculation
This calculator determines the required wire gauge by checking both the ampacity limit and ensuring the voltage drop remains below the safe threshold of 3%. The core formula used to calculate voltage drop is:
- VD (Voltage Drop): The amount of voltage lost over the cord length.
- K (Specific Resistance): A constant for the conductor material. For copper, this is typically 12.9 ohms-cmil/ft.
- L (Length): The one-way length of the extension cord in feet. We multiply by 2 because the current must travel down the hot wire and back on the neutral wire.
- I (Current): The load in Amperes (Amps) drawn by your tool or appliance.
- CM (Circular Mils): The cross-sectional area of the wire. A thicker wire (lower AWG number) has a higher CM, which reduces resistance and voltage drop.
Why It Matters
If the voltage drop exceeds 3% to 5%, the motor in your tool has to pull more current to compensate for the lower voltage. This excess current creates heat, which can melt the cord's insulation, create a fire hazard, or permanently damage the tool's motor.
Safety Rules
- Never Daisy Chain: Plugging extension cords into each other increases resistance and fire risk.
- Uncoil Fully: Using a cord while coiled can create an inductor, causing heat buildup and melting insulation.
- Check Temperature: If the cord feels warm to the touch, it is undersized. Stop using it immediately.