Wire gauge comparisons

Between two neighbouring gauges the ampacity table often allows either, and the thing that actually decides is how long the run is. Resistance rises as the wire thins, and the voltage lost along the way rises with it — which is why the answer to "12 or 14?" depends on a distance nobody mentions.

Each page gives the drop at four run lengths and the distance each gauge reaches before losing 3% of a 120 V supply.

Where these numbers come from

Diameter comes from the AWG definition, d = 0.005 × 92^((36 − n)/39) inches, checked against fifteen published figures on every build. Resistance uses the IACS annealed-copper value of 1.724×10⁻⁸ Ω·m, which is what wire tables in print reproduce. Ampacities are the NEC 310.16 60 °C copper column.

Sizing a circuit is not arithmetic. Insulation type, ambient temperature, conductor count, breaker rating and local code all bear on what a wire may carry, and none of that is on these pages. They give the physics; the circuit is an electrician's decision.

All 23 comparisons

Full wire gauge chart