How does this determine appropriate wire gauge?

Matching expected current load and wire length against ampacity tables.

Why does a lower gauge number mean a thicker wire?

AWG numbering is inversely related to diameter by convention.

Why does wire length affect the gauge needed?

Longer runs have more resistance, often requiring a thicker wire for safe delivery.

Wire Gauge / Ampacity Calculator

Wire gauge (AWG) determines how much current a wire can safely carry without overheating — thicker wires (lower AWG numbers) carry more current.

Wire Gauge (AWG)

Insulation Temp Rating (°C)

Instant Result

Safe Ampacity (Copper) -

What Is a Wire Gauge / Ampacity Calculator?

Wire gauge (AWG) determines how much current a wire can safely carry without overheating — thicker wires (lower AWG numbers) carry more current. This calculator provides reference ampacity values for common copper wire gauges at standard insulation temperature ratings, based on published NEC reference tables.

How to Use This Wire Gauge / Ampacity Calculator

Enter the wire's AWG gauge (common sizes: 14, 12, 10, 8, 6, 4, 3, 2, or 1).
Enter the insulation's temperature rating (60°C, 75°C, or 90°C — printed on the cable jacket).
Click Calculate to see the reference safe ampacity for that wire.
This is for general reference only — always follow your local electrical code and consult a licensed electrician for actual installations, since factors like ambient temperature, bundling, and run length also affect the safe rating.

Formula

Ampacity values are standard reference lookups (copper conductor, based on NEC Table 310.16), not a formula.

Worked Example

A standard 12 AWG copper wire with 75°C-rated insulation has a reference ampacity of about 25 amps — the size commonly used for household 20-amp circuits, with a safety margin.