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Electrical Wire Size Calculator

Determine the correct wire gauge for your electrical project based on amperage, distance, voltage, and NEC requirements.

How to Use This Calculator

1. Enter the circuit amperage (check your breaker or appliance rating). 2. Select the voltage (120V for standard outlets, 240V for dryers/ranges, 208V/480V for commercial). 3. Enter the one-way distance from the panel to the load in feet. 4. Choose single-phase (residential) or three-phase (commercial). 5. Select copper or aluminum wire material. 6. Set max voltage drop % (3% is standard NEC recommendation). 7. Click Calculate to see the recommended wire gauge.

How to Select the Right Wire Size for Any Electrical Circuit

Choosing the correct wire gauge is critical for electrical safety and code compliance. Wire that is too small for the current it carries can overheat, damage insulation, and cause fires. The National Electrical Code (NEC) provides strict guidelines for wire sizing based on ampacity and voltage drop.

Wire size in North America is measured using the American Wire Gauge (AWG) system, where smaller numbers indicate larger wires. Common residential sizes include 14 AWG (15-amp circuits), 12 AWG (20-amp circuits), 10 AWG (30-amp circuits for dryers/AC), and 8 AWG (40-amp circuits for ranges).

Two factors determine minimum wire size: ampacity and voltage drop. Ampacity is the maximum current a wire can safely carry without overheating. The NEC requires that continuous loads (running 3+ hours) use only 80% of the wire's rated ampacity — so a 20-amp continuous load requires wire rated for 25 amps.

Voltage drop becomes critical for long wire runs. The NEC recommends no more than 3% voltage drop for branch circuits and 5% total from the service panel. A 3% drop on a 120V circuit means only 3.6V loss. On a 100-foot run, this might require upsizing from 12 AWG to 10 AWG.

Copper wire is the standard for most residential applications due to its superior conductivity. Aluminum wire costs less and is commonly used for service entrance cables and long feeder runs. When using aluminum, you must upsize by approximately 2 gauge numbers compared to copper for equivalent ampacity.

Frequently Asked Questions

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

12 AWG copper wire is required for a 20-amp circuit. For runs over 50 feet, consider upsizing to 10 AWG to minimize voltage drop. Always use 20-amp rated outlets and a 20-amp breaker with 12 AWG wire.

How do I calculate voltage drop?

Voltage drop = (2 × Length × Resistance × Current) / 1000 for single-phase circuits. Length is the one-way distance in feet, resistance is per 1000 feet of wire, and current is in amps. Keep total drop under 3% for branch circuits.

Can I use aluminum wire instead of copper?

Yes, but you must upsize the wire. Aluminum has about 60% the conductivity of copper, so where you would use 10 AWG copper, you would need 8 AWG aluminum. Aluminum requires special connectors rated for aluminum to prevent corrosion issues.

What wire size do I need for a 240V circuit?

It depends on the amperage, not just voltage. A 30-amp 240V circuit (dryer) needs 10 AWG copper. A 40-amp circuit (range) needs 8 AWG. A 50-amp circuit (large range/welder) needs 6 AWG. Always check NEC tables for your specific application.