Wire Gauge Calculator

Find the recommended AWG wire gauge based on current, distance, and acceptable voltage drop.

A
ft

Distance from panel to load (not round-trip)

%

NEC recommends 3% for branch circuits

Recommended AWG

—

Minimum wire size

Max Ampacity

—

NEC rated capacity

Actual Voltage Drop

—

At recommended gauge

Voltage Drop %

—

Of system voltage

Wire Resistance

—

Round-trip total

Voltage at Load

—

After drop

Wire Sizing Guide

NEC Wire Sizing Rules

The National Electrical Code requires wire to be sized for both ampacity (current-carrying capacity) and voltage drop. The wire must satisfy both requirements — always use the larger of the two sizes.

  • Ampacity: Wire must be rated to safely carry the circuit current without overheating
  • Voltage drop: NEC recommends max 3% drop for branch circuits, 5% total including feeder

Common Household Circuits

Circuit Amps Typical AWG
Lighting 15A 14 AWG
General outlets 20A 12 AWG
Dryer / AC unit 30A 10 AWG
Range / Oven 40-50A 6-8 AWG
Service entrance 100-200A 1-4/0 AWG

Safety Considerations

  • Always size wire for the breaker rating, not the expected load
  • Derate ampacity for conduit fill, ambient temperature, and bundling
  • Use THHN/THWN rated wire for most residential applications
  • Longer runs almost always need upsizing for voltage drop

Copper vs Aluminum

This calculator uses copper wire values. For aluminum wire, go up 2 AWG sizes (e.g., if copper calls for 10 AWG, use 8 AWG aluminum). Aluminum requires anti-oxidant compound and rated connectors.

Disclaimer: Always consult a licensed electrician and follow local electrical codes. This calculator provides estimates for planning purposes only.

Frequently Asked Questions

Why does wire gauge matter?
Using wire that is too small for the current it carries creates excessive resistance, which causes voltage drop and heat buildup. Voltage drop reduces the performance of connected equipment (dim lights, slow motors), while excessive heat can melt insulation and cause fires. The National Electrical Code (NEC) specifies minimum wire sizes for safety.
What is acceptable voltage drop?
The NEC recommends no more than 3% voltage drop for branch circuits and 5% total for feeders plus branch circuits combined. For sensitive electronics, 2% or less is preferred. Long runs of wire (like to a detached garage or well pump) are especially prone to voltage drop and may require larger wire than the ampacity alone suggests.
What is the difference between copper and aluminum wire?
Copper has about 60% better conductivity than aluminum, so aluminum wire must be larger (typically 2 AWG sizes up) to carry the same current. Copper is more commonly used in residential wiring due to its better conductivity and easier termination. Aluminum is common in service entrance cables and utility lines because it is lighter and cheaper for large gauges.
What does AWG stand for?
AWG stands for American Wire Gauge, the standard system for measuring wire diameter in North America. Counter-intuitively, smaller numbers mean thicker wire. AWG 14 is common for 15-amp household lighting circuits, AWG 12 for 20-amp outlets, and AWG 10 for 30-amp dryer circuits. For wires thicker than 1 AWG, the system switches to 1/0 (one-ought), 2/0, 3/0, and 4/0.

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