Wire Gauge Calculator
Find the correct AWG wire size for any circuit. Enter load and run length to get recommended gauge, voltage drop, and ampacity instantly.
Last reviewed: June 2026AWG Reference Table
Copper and aluminum resistance at 20-C; NEC ampacity for conductors in conduit (75-C rating, 30-C ambient, 3 conductors max).
| AWG | Diameter (in) | Cu Ω/1000ft | Al Ω/1000ft | Cu Ampacity | Al Ampacity |
|---|
How the Wire Gauge Calculator works
This calculator chooses an American Wire Gauge size from the load current, one-way wire distance, system voltage, maximum voltage drop, and conductor material. It doubles the distance to model the full round-trip circuit, calculates conductor resistance from the AWG reference table, and checks each gauge against both voltage drop and the 75 C ampacity value in the table.
The voltage-drop formula is drop volts = amps * ohms per foot * round-trip feet. The calculator converts that into a percentage of system voltage, then reports power lost in the wire as amps^2 * resistance. It selects the smallest listed gauge that satisfies both the requested voltage-drop limit and the ampacity limit. If no listed gauge passes, it shows the largest available gauge in the table.
Choosing inputs
- Current: Enter the expected continuous load in amps. For code work, use the load value after any required derating.
- Distance: Enter one-way run length in feet from source to load. The calculator handles the return path internally.
- Voltage: Choose 12 V, 24 V, 120 V, or 240 V. Low-voltage systems are more sensitive to the same voltage drop.
- Max voltage drop: A 3% target is common for branch-circuit planning; 5% can be acceptable for less sensitive runs.
- Material: Copper and aluminum use different resistance and ampacity columns.
How to read the result
The recommended AWG is the first gauge in the table that meets both checks. The voltage-drop tile shows actual drop in volts and percent, the power-loss tile shows heat wasted in the conductor, the resistance tile shows total round-trip resistance, and the ampacity tile tells whether the entered load is within the table rating.
Example
For a 20 A load, 50 ft one-way run, 120 V system, 3% maximum drop, and copper conductor, 14 AWG and 12 AWG do not meet the 3% drop target over the full 100 ft round trip. The calculator moves up to 10 AWG, which keeps voltage drop below the target and has enough ampacity in the reference table.
Common mistakes
- Entering round-trip distance: Enter one-way distance only; the calculator doubles it.
- Checking voltage drop but not ampacity: A conductor must pass both the voltage-drop target and the current rating.
- Using aluminum like copper: Aluminum has higher resistance and different ampacity values, so it often needs a larger gauge.
- Treating this as a permit design: Local code, insulation type, conduit fill, ambient temperature, terminals, and derating can change the required conductor size.