Wire Size Calculator
Calculate the correct electrical wire gauge for your circuit based on amperage, distance, and voltage drop requirements. NEC compliant sizing for copper and aluminum wire.
How to Use This Calculator
Calculate proper wire size for electrical circuits:
- Enter the circuit amperage (breaker size or load current)
- Enter the one-way wire distance in feet from panel to load
- Select voltage (120V standard, 240V for heavy appliances)
- Choose wire material (copper or aluminum)
- Select acceptable voltage drop percentage (3% recommended)
Why This Matters
Wire sizing affects both safety and performance. Undersized wire overheats, creating fire hazards. Wire adequate for ampacity but undersized for distance causes voltage drop, making motors struggle and lights dim.
- Size wire for both ampacity and voltage drop
- Compare copper vs aluminum options
- Ensure NEC code compliance
- Estimate wire cost for your run
Worked Examples
20-Amp Kitchen Circuit
60 feet from panel, 120V copper wire
Calculation: By ampacity: 12 AWG. Voltage drop: 3.2% (exceeds 3%)
Result: 10 AWG recommended for optimal performance
100-Amp Subpanel Feed
150 feet, 240V aluminum wire
Calculation: By ampacity: 1 AWG. By voltage drop: 2/0 needed
Result: 2/0 aluminum to stay under 3% drop
Common Mistakes to Avoid
- Using only ampacity tables and ignoring voltage drop for long runs
- Forgetting wire distance is round-trip (already calculated)
- Confusing circuit breaker size with actual load
- Using copper ampacity values for aluminum wire
- Forgetting 80% derating for continuous loads (3+ hours)