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Electrical Wire Size Calculator

Calculate proper wire gauge (AWG) for safe electrical installations
Safety Warning: Electrical work can be dangerous. Always follow NEC codes and hire a licensed electrician for installations.
Continuous load current
One-way distance from panel to load
NEC recommends 3% max (5% total)

Enter electrical requirements to calculate wire size.

Wire Size Calculator Guide

How to Calculate Wire Size

1. Determine Load Amperage

Calculate or measure the current draw of your electrical load. For continuous loads (running 3+ hours), use actual amperage.

2. Measure Wire Length

Measure one-way distance from electrical panel to the load. The calculator accounts for round-trip resistance.

3. Check Ampacity

Wire must handle 125% of continuous load (NEC requirement). Example: 20A load needs wire rated for 25A minimum.

4. Calculate Voltage Drop

NEC recommends max 3% voltage drop for branch circuits, 5% total. Longer runs need larger wire.

Common Wire Sizes

  • 14 AWG: 15A circuits (lights, outlets)
  • 12 AWG: 20A circuits (kitchen, bathroom)
  • 10 AWG: 30A circuits (dryer, water heater)
  • 8 AWG: 40-50A circuits (range, large AC)
  • 6 AWG: 55-65A circuits (sub-panels)
Pro Tips
  • NEC 125% Rule
    For continuous loads (3+ hours), multiply amperage by 1.25 before sizing wire.
  • Voltage Drop
    Keep under 3% for efficiency. Use larger wire for long runs.
  • Copper vs Aluminum
    Aluminum is cheaper but needs larger gauge. Copper is preferred for most applications.
AWG Wire Gauge

American Wire Gauge (AWG) is the standard for wire sizing in North America.

Remember: Smaller AWG number = Thicker wire = Higher ampacity

Frequently Asked Questions

Q: What is AWG wire gauge?

A: American Wire Gauge (AWG) is the standard system for measuring wire diameter in North America. Smaller AWG numbers indicate thicker wires with higher current capacity. For example, 10 AWG is thicker than 14 AWG.

Q: Why does the NEC require 125% of load amperage?

A: The National Electrical Code requires wire to handle 125% of continuous loads (operating 3+ hours) to prevent overheating and ensure safety. This safety margin accounts for heat buildup during extended operation.

Q: What is voltage drop and why does it matter?

A: Voltage drop is the reduction in voltage as electricity travels through wire. Excessive voltage drop (>3-5%) causes motors to overheat, lights to dim, and appliances to malfunction. Longer wire runs need larger wire to minimize voltage drop.

Q: Can I use aluminum wire instead of copper?

A: Yes, but aluminum requires a larger gauge (typically 2 sizes bigger) to match copper's ampacity. Aluminum is cheaper but requires special connectors and installation techniques. Copper is generally preferred for residential wiring.

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

A: For a 20A circuit, use 12 AWG copper wire minimum. This provides 20A ampacity at 75°C rating. For long runs (>50 feet), consider 10 AWG to reduce voltage drop.

Q: Do I need a licensed electrician for electrical work?

A: Yes! Most jurisdictions require licensed electricians for electrical installations. Improper wiring can cause fires, electrocution, and code violations. Always hire a licensed professional and obtain proper permits.

Disclaimer

CRITICAL SAFETY WARNING:

  • This calculator provides estimates only for educational purposes. Actual wire sizing must comply with local electrical codes and NEC requirements.
  • ELECTRICAL WORK IS DANGEROUS. Improper wiring can cause fires, electrocution, property damage, and death. Always hire a licensed electrician for electrical installations.
  • This tool uses simplified calculations. Professional electrical design considers many additional factors including: ambient temperature, conduit fill, bundling derating, terminal temperature ratings, and specific NEC articles.
  • Wire sizing must comply with National Electrical Code (NEC) and local building codes. Requirements vary by jurisdiction.
  • This calculator assumes 75°C wire temperature rating and standard installation conditions. Different conditions require different sizing.
  • Permits required: Most electrical work requires permits and inspections. Unpermitted work is illegal and dangerous.
  • Aluminum wire requires special installation techniques and anti-oxidant compound. Improper aluminum connections can cause fires.
  • Cost estimates are approximate and vary by location, wire type, and market conditions.
  • This tool does not account for: conduit fill limits, derating factors, special conditions, or specific NEC exceptions.
  • We are not responsible for any errors, omissions, injuries, fires, property damage, code violations, or other consequences resulting from the use of this calculator.

ALWAYS consult with licensed electricians and follow all applicable electrical codes. Your safety depends on it.

Wire Size Calculator

Calculate the correct electrical wire gauge (AWG) for safe installations. Accounts for ampacity and voltage drop!

Wire Basics
AWG System Smaller number = Thicker wire
NEC 125% Rule Continuous loads need 25% extra capacity
Voltage Drop Max 3% recommended (5% total)
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Electrical Wire & Safety:

Did You Know?

Electrical fires cause an estimated $1.3 billion in property damage annually in the US. Proper wire sizing is critical for safety!