Every gauge, both units, and the metric size you can actually order.
A wire gauge gives you a diameter. It does not give you a cable size, and the gap between those two things is where most conversion mistakes happen.
12 AWG measures 2.05 mm across and has a cross-section of 3.31 mm². Both numbers are correct and both get asked as “12 AWG in mm.” The first is what you need for ferrules, glands and terminal ranges. The second is what you need for a cable schedule — and it is not a size anyone manufactures, so it needs converting again before it is useful.
Each page below gives all three: the diameter, the cross-section, and the metric size to specify. Plus the conductor resistance, the stranded and flexible diameters at that size, and how much copper you gain or lose by rounding either way.
Every gauge
| Gauge | Diameter | Cross-section | Metric size | Change |
|---|---|---|---|---|
| 4/0 AWG | 11.684 mm | 107.2 mm² | 120 mm² | +12% |
| 3/0 AWG | 10.404 mm | 85.0 mm² | 95 mm² | +12% |
| 2/0 AWG | 9.26 mm | 67.4 mm² | 70 mm² | +4% |
| 1/0 AWG | 8.25 mm | 53.5 mm² | 70 mm² | +31% |
| 2 AWG | 6.54 mm | 33.6 mm² | 35 mm² | +4% |
| 4 AWG | 5.19 mm | 21.1 mm² | 25 mm² | +18% |
| 6 AWG | 4.11 mm | 13.3 mm² | 16 mm² | +20% |
| 8 AWG | 3.26 mm | 8.37 mm² | 10 mm² | +19% |
| 10 AWG | 2.59 mm | 5.26 mm² | 6 mm² | +14% |
| 12 AWG | 2.05 mm | 3.31 mm² | 4 mm² | +21% |
| 14 AWG | 1.63 mm | 2.08 mm² | 2.5 mm² | +20% |
| 16 AWG | 1.29 mm | 1.31 mm² | 1.5 mm² | +15% |
| 18 AWG | 1.02 mm | 0.823 mm² | 1 mm² | +22% |
| 20 AWG | 0.813 mm | 0.519 mm² | 0.75 mm² | +45% |
| 22 AWG | 0.643 mm | 0.324 mm² | 0.5 mm² | +54% |
| 24 AWG | 0.511 mm | 0.205 mm² | 0.5 mm² | +144% |
| 26 AWG | 0.404 mm | 0.128 mm² | 0.5 mm² | +291% |
For gauges not listed here, and for the full range down to 44 AWG, use the AWG converter.
Read the change column
That last column is the part worth studying. It shows how much extra copper you buy when you round up to the nearest metric size, and it is nowhere near constant.
At 2/0 and 2 AWG the step is 4% — those two gauges line up with metric sizes almost exactly, and they are the only ones that satisfy the metric conductor resistance limit.
At 1/0 the step is 31%, because 53.5 mm² just clears 50 and has to go to 70. That is the worst value in the common range.
Below 20 AWG the metric series runs out of resolution entirely. 24 AWG converts to 0.205 mm², and the smallest metric size is 0.5 — more than double.