Wire Gauge Charts Editorial · October 6, 2026
AWG vs metric: every odd-size question, answered with mm²
If you order wire in North America you buy AWG sizes. Practically everywhere else — Europe, South America, Asia, Australia — you buy metric cross-sections listed in mm². Both describe the same physical conductor, so the two systems map onto each other — but loosely, and that looseness causes most of the confusion.
Why the numbers never match exactly
AWG comes out of a geometric progression: diameter shrinks by a factor of ⁹²√ with each gauge step. Metric sizes are a practical ladder that standards committees picked: 0.5, 0.75, 1, 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185, 240 mm²…
Because the ladders step differently, an AWG size rarely equals a metric size exactly. The common workhorse pairs look like this:
| AWG | mm² (exact) | Nearest metric size | Difference |
|---|---|---|---|
| 10 | 5.26 | 6 mm² | +14% |
| 12 | 3.31 | 3 mm²* / 4 mm² | −9% / +21% |
| 14 | 2.08 | 2 mm²* / 2.5 mm² | −4% / +20% |
| 16 | 1.31 | 1.25 mm²* / 1.5 mm² | −5% / +14% |
| 18 | 0.82 | 0.75 mm² | −8% |
*Some cable cultures keep half-step sizes (3 mm², 2 mm², 1.25 mm²) that mainstream IEC lists no longer feature.
The rule: round up for power, don’t bother for signals
When the metric cable will carry circuit current, the safe move is up: pick the first metric size at or above the AWG cross-section. A 12 AWG circuit (3.31 mm²) gets a 4 mm² metric cable, because going down to 3 mm² removes ampacity headroom you may need for grouping and temperature derating.
For signal work the economics flip. A speaker run or sensor lead cares about resistance per length, not ampacity; the nearest size in either direction is usually fine, and the smaller cable is easier to route.
Resistance is the real bridge
Cross-section is only the visible difference. The quantity that predicts voltage drop and heating is resistance — and since R = ρL/A, equal area means equal resistance regardless of what unit system labels it. A 6 mm² metric wire and its nearest AWG cousin delay current identically over the same length.
That’s why our charts show Ω/km alongside Ω/1000 ft: pick whichever length unit you think in, the physics is the same.
One gotcha: stranded vs solid
Two cables with the same nominal mm² can differ in real copper area because standards allow different strand counts (a concealed “reduced-strand” arrangement packs the same mm² into thinner outer diameter). Trust measured resistance over printed mm² if the stakes are high — the copper wire gauge chart produces its Ω values straight from cross-section, which makes it the fastest sanity check between the two unit systems.