Wire Size Calculator
Choosing the right wire size prevents overheating, voltage drop problems, and code violations. Enter your circuit's amperage, distance, and voltage, and this calculator tells you the smallest AWG gauge that keeps voltage drop within your chosen limit. It covers copper and aluminum wire in both single-phase and three-phase configurations.
How it works:
The calculator checks each wire gauge starting from 14 AWG and finds the first one where the voltage drop stays within your selected limit (2%, 3%, or 5%).
Voltage drop formula:
- Single phase: Vdrop = 2 × I × R × L/1000
- Three phase: Vdrop = √3 × I × R × L/1000
Where I is current in amps, R is resistance per 1,000 feet for the wire gauge, and L is the one-way distance in feet.
NEC guidelines:
- 3% max for branch circuits (outlets, lights, appliances)
- 5% max for the combined feeder and branch circuit
These are recommendations, not hard code requirements, but following them avoids problems like dimming lights, slow-starting motors, and wasted energy.
Copper vs. aluminum:
Aluminum has about 61% of copper's conductivity, so it needs to be about 1.6 times thicker (roughly two gauge sizes larger) for the same performance. Aluminum is lighter and less expensive per foot, making it popular for long runs and service entrance cables.
Example: A 20A circuit on 120V with a 150-foot run needs at least 8 AWG copper to stay under 3% drop. Using 12 AWG on that run would result in nearly 6% drop.