10 Gauge Wire in mm: Diameter, mm2 and Ampacity

10 gauge wire measures 2.59 mm across. Its cross-section is 5.26 mm², or 10,380 circular mils.

The metric size that replaces it is 6 mm², which is 14% more copper — one of the smaller round-up penalties in the range.

Ampacity, and the limit that overrides it

10 AWG copper carries 30 A at 60 °C, 35 A at 75 °C, and 40 A at 90 °C, based on not more than three current-carrying conductors at 30 °C ambient.

Then there is the part that catches people out. 10 AWG carries a footnote in the ampacity table pointing to the overcurrent protection rules, which cap the device at 30 A regardless of what the 90 °C column says. So a 90 °C conductor rated 40 A still sits behind a 30 A breaker.

The higher columns are not useless — they are what you derate from. If a 90 °C conductor is derated for ambient and grouping down to 33 A, it still supports a 30 A circuit. Start from the column matching your insulation, apply the corrections, then apply the cap.

The metric equivalent at 6 mm², three loaded conductors clipped direct to a wall at 30 °C:

The metric column reads higher because 6 mm² has 14% more copper, not because the metric rules are looser. The two systems define installation methods and derating differently, so treat these as parallel answers rather than a conversion.

Derating a real circuit

The table figure assumes 30 °C ambient and three loaded conductors. Neither holds inside a hot panel.

Take 6 mm² PVC, clipped direct, in a 45 °C enclosure with three circuits bunched together:

41 A × 0.79 (45 °C) × 0.70 (3 circuits) = 22.7 A

The 41 A conductor is a 22.7 A conductor in that installation — a 45% reduction, and it happened without changing the cable. This is why “how many amps does 10 gauge carry” has no single answer.

The correction factors that matter most:

Grouping bites harder than temperature. Two bunched circuits is 0.80, three is 0.70, six is 0.57.

Voltage drop is usually what sizes 10 AWG

10 AWG rarely gets chosen because 12 AWG could not carry the current. It gets chosen because the run is long.

A 10 AWG conductor runs about 3.28 Ω/km. A 40 m out-and-back circuit is 80 m of conductor, or 0.26 Ω. At 25 A that is 6.6 V — about 5.5% on a 120 V supply, which is past most voltage drop allowances.

Going from 12 AWG to 10 AWG cuts the resistance from 5.21 to 3.28 Ω/km, a 37% reduction. That is the reason to step up on a long run, and it has nothing to do with the ampacity table.

10 AWG does not pass as 6 mm²

Metric cable is verified by conductor resistance, not by measuring copper. The limit for 6 mm² is 3.08 Ω/km, and 10 AWG measures 3.28.

10 AWG misses by about 6% — the closest near-miss of any common gauge, but still a miss. Only 2 AWG and 2/0 clear their metric limits, for the reason explained in why AWG doesn’t match metric sizes.

Rounding down to 4 mm² costs 24% of the cross-section, which on a long run is exactly the wrong direction.

Conductor diameter

2.59 mm is solid wire. At 6 mm², the maximums by construction:

Class 5 is 51% wider than solid 10 AWG. That is the largest relative spread in the branch-circuit range, and it matters for ferrules and glands. See conductor classes 1, 2, 5 and 6.

Where 10 AWG is used

30 A circuits — water heaters, larger air conditioners, ranges on smaller services, and sub-feeds. It is also the default when a 20 A circuit runs far enough that 12 AWG drops too much voltage.

In PV work it is common on string and combiner runs, where the run length rather than the current drives the choice.

FAQ

How many mm is 10 gauge wire? 2.59 mm in diameter for solid wire, which is 101.9 mils. Stranded 10 AWG measures wider.

What is 10 AWG in mm²? 5.26 mm². The metric cable size to order is 6 mm², which is 14% larger.

How many amps can 10 gauge wire carry? 30 A at 60 °C, 35 A at 75 °C, 40 A at 90 °C, before derating. In practice the overcurrent device is capped at 30 A regardless. Correct for ambient temperature and conductor grouping in your actual installation.

Is 10 AWG the same as 6 mm²? No. 6 mm² has 14% more copper, and a 10 AWG conductor misses the 6 mm² resistance limit by about 6%.

Can I use 4 mm² instead of 10 AWG? It is 24% less copper and a higher resistance per metre. On the long runs where 10 AWG is usually chosen, that is the wrong direction.

Is 10 gauge or 12 gauge thicker? 10 gauge. Lower AWG numbers are thicker. 10 AWG is 2.59 mm against 2.05 mm and has 59% more copper.

Reference

Work the other direction from 6 mm² to AWG, or use the converter.