WIRE SIZE CALCULATOR

Wire Size Calculator — Find the Right AWG Gauge for Any Circuit

Find the minimum AWG wire gauge for single-phase and three-phase circuits based on load current, one-way run length, voltage and maximum allowable voltage drop. Results comply with NEC 310.15 ampacity tables for copper and aluminum conductors.

System type

Circuit parameters

Conductor material

Recommended wire size
—AWG

Enter circuit details to calculate.

How Wire Size Is Determined

Selecting the correct wire size involves satisfying two independent criteria — the larger wire required by either criterion must be used:

  1. Ampacity: The wire must carry the load current without overheating. Set by NEC 310.15 tables based on conductor type, insulation rating and installation method.
  2. Voltage drop: The wire must be large enough to keep voltage drop within acceptable limits (typically ≤3% for branch circuits).

Long runs almost always require a larger wire for voltage drop reasons even when the ampacity requirement is met by a smaller gauge.

AWG Wire Size Quick Reference (Copper, 60°C)

  • #14 AWG: 15 A — lighting and receptacle branch circuits
  • #12 AWG: 20 A — kitchen, bathroom and general outlets
  • #10 AWG: 30 A — dryers, water heaters, A/C units
  • #8 AWG: 40 A — ranges, large air conditioners
  • #6 AWG: 55 A — sub-panels, EV chargers (Level 2)
  • #4 AWG: 70 A — large sub-panels and motors
  • #2 AWG: 95 A — service entrance, large sub-panels

Copper vs Aluminum Wire

Both copper and aluminum are code-compliant conductors, but they have important differences to understand before specifying:

  • Aluminum has about 61% the conductivity of copper, so requires one size larger for the same ampacity
  • Aluminum expands and contracts more with temperature — requires anti-oxidant compound and AL-rated connectors
  • Aluminum is significantly cheaper and lighter, making it the standard choice for service entrance and large feeder conductors
  • Copper is preferred for branch circuit wiring due to ease of termination and reliability

Frequently Asked Questions

What wire size do I need for a 20-amp circuit?

#12 AWG copper wire is required for a 20-amp branch circuit. #14 AWG is only rated for 15-amp circuits and cannot be used on a 20-amp breaker.

What size wire for a 100-amp sub-panel 150 feet away?

For a 100-amp feeder at 150 ft with 240V single-phase, #1 AWG copper or #2/0 AWG aluminum is typically required to keep voltage drop under 3%. Always verify with a licensed electrician.

Does conduit fill affect wire ampacity?

Yes. When more than 3 current-carrying conductors share a conduit, ampacity must be derated per NEC 310.15(C). This calculator does not apply conduit fill derating — consult an electrician for multi-conductor installations.

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