Wire Gauge Calculator
Choosing the right wire gauge ensures safety and code compliance. This calculator checks both NEC ampacity requirements and voltage drop to recommend the correct wire size.
Enter Your Measurements
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How to Use This Calculator
- Enter the load current in amps.
- Select circuit voltage.
- Enter one-way wire distance in feet.
- Indicate if the load is continuous (runs 3+ hours).
- Review the recommended wire gauge.
How Wire Gauge Calculation Works
Wire sizing must satisfy two independent requirements: ampacity (the wire must safely carry the current without overheating) and voltage drop (must stay under 3% per NEC recommendation). This calculator checks both and recommends the larger (more conservative) gauge. For continuous loads, NEC requires sizing wire and breaker at 125% of the load current. Ampacity values are from NEC Table 310.15 for copper conductors at 60°C.
Formula
Ampacity sizing: Required ampacity = Load × continuous factor (1.25 if continuous). Then find smallest AWG that meets both ampacity and ≤3% voltage drop requirements.
Frequently Asked Questions
What wire size for a 20-amp circuit?
What's the difference between ampacity and breaker size?
When do I need to use the 125% continuous load rule?
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