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Enter your circuit's current and wire run to get a recommended copper wire gauge.
Wire that's too thin for the current it carries overheats, which is a fire risk, and wastes power as voltage drop, so lights dim and motors struggle at the far end of a long run. Picking a gauge means checking two things: that the wire can safely carry the current (ampacity), and that the voltage lost over the length of the run stays acceptably low.
In the American Wire Gauge system, smaller numbers mean thicker wire. Every 3 gauge steps roughly doubles the copper's cross-section and halves its resistance. Typical 60°C copper ratings used as a general reference:
Voltage drop = current × resistance of the round-trip length (out and back), shown as a percentage of supply voltage. A common guideline is to keep it within about 3% for a branch circuit.
A 15 A load, 50 ft one-way run at 120 V:
On long runs, voltage drop rather than ampacity often decides the gauge.
Only as general background. Installation rules depend on cable type, insulation, how it's run and bundled, and local codes such as the NEC in the US or AS/NZS 3000 in New Zealand and Australia. In many countries fixed household wiring must legally be done by a licensed electrician.
The same power at a lower voltage needs more current, and every volt lost is a bigger share of the total. A 12 V solar, caravan or boat system needs much heavier cable than a 230 V circuit for the same load.
Aluminium has about 60% of copper's conductivity, so it needs a larger gauge (typically about two AWG sizes bigger) for the same current. It also needs compatible connectors. This calculator assumes copper.
Wire must be rated at least as high as the breaker or fuse protecting it, because the breaker protects the wire. For continuous loads, codes commonly size for 125% of the load current.