Wire Gauge Calculator

Find the correct AWG wire gauge based on load, wire length and voltage drop limits.

Recommended AWG
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Ampacity
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amps
Actual Voltage Drop
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%
Voltage Drop
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volts

AWG Reference Table

Gauge Ampacity Voltage Drop (%) Voltage Drop (V)

How the Wire Gauge Calculator Works

This calculator selects the smallest AWG copper wire that satisfies two NEC criteria: ampacity (current-carrying capacity) must be at or above your load in amps, and voltage drop must be at or below your specified maximum. Voltage drop is calculated using the formula VD = (2 × L × R × I) ÷ 1000, where L is the one-way wire length in feet and R is the resistance in ohms per 1,000 feet from NEC Table 9. The factor of 2 accounts for both the hot and neutral conductor. The NEC recommends keeping voltage drop below 3% for branch circuits and 5% total for feeder plus branch. The table shows all AWG sizes so you can compare options for your specific run length and load.

Frequently Asked Questions

What wire gauge do I need for a 20-amp circuit?
12 AWG copper wire is required for a 20-amp circuit per NEC 210.19. Use 10 AWG for runs over 50 feet to limit voltage drop to 3%.
What is voltage drop and why does it matter?
Voltage drop is the reduction in voltage along a wire due to resistance. The NEC recommends keeping it under 3% for branch circuits and 5% total (feeder + branch).
What is the ampacity of 12 AWG wire?
12 AWG copper in conduit has an ampacity of 20 amps at 60°C per NEC Table 310.15(B)(16).
Can I use aluminum wire instead of copper?
Yes, but aluminum has higher resistance and requires larger gauge for the same ampacity. Always use anti-oxidant compound on aluminum connections and use approved connectors.

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