AWG Wire Size Chart: Circular Mils, Resistance & Ampacity

How to read the AWG chart

American Wire Gauge numbering runs backwards: the smaller the gauge number, the thicker the conductor. Each three-step drop in gauge (for example 12 → 9) roughly doubles the cross-sectional area, and the very large sizes switch to the "aught" notation — 1/0, 2/0, 3/0, 4/0, read "one-aught" and so on, each thicker than 1 AWG. The circular mils column is the true measure of that cross-section, and it is the value the voltage-drop formula uses directly.

The resistance columns give ohms per 1,000 feet for copper and aluminum. Aluminum shows roughly 1.6 times the resistance of copper for the same gauge, which is why an aluminum run either drops more voltage or needs a larger conductor for the same job. The ampacity column shows the NEC 310.16 allowable current at the common 75 °C termination rating; use it as a starting point, then apply the full ampacity table derating for temperature and bundling.

In practice you read the chart in one of two directions. Working forward, you have a gauge and want its properties. Working backward — the usual case — you have a required cross-section from the Wire Size calculator and step up to the next real gauge that meets or exceeds it. Never round down to a thinner wire to save cost. For the method behind the numbers, read the AWG wire-gauge chart explained.