1/0 AWG in mm: Why Rounding Up Costs 31% Here

1/0 AWG measures 8.25 mm across. Its cross-section is 53.5 mm², or 105,600 circular mils.

This gauge has the worst round-up penalty in the entire range, and it is worth understanding before you specify anything.

53.5 mm² falls in the wrong place

The metric series jumps from 50 mm² straight to 70 mm². Nothing exists between them.

1/0 converts to 53.5 mm², which clears 50 by 7% and then has nowhere to go but 70:

31% is the largest round-up penalty of any gauge on this site. For comparison, 2/0 one size up rounds to 70 mm² for just 4%, and 4/0 rounds up for 12%.

If 1/0 had converted to 49 mm² instead of 53.5, it would round to 50 and cost you 2%. It missed by three and a half square millimetres and the penalty is a third of the conductor.

The resistance test says take 50 mm²

A 1/0 conductor runs about 0.322 Ω/km.

1/0 satisfies the 50 mm² requirement with margin. It is nowhere near meeting 70 mm².

So both the arithmetic and the test point downward. 50 mm² is the match, and it is 7% smaller — the kind of gap that disappears inside normal design margin.

This is the feeder-scale equivalent of what happens at 20 AWG, where the size below is 4% away and the size above is 45% more. When the metric series has a wide step, the conductor lands near the bottom of it and rounding up stops making sense.

Check the ampacity before you commit

The resistance test clearing 50 mm² does not automatically mean the circuit does.

50 mm² PVC at 144 A sits slightly under the 150 A of 1/0 at the 75 °C rating. On XLPE it is comfortably above. So the answer depends on the insulation as much as the size.

Run the numbers for the actual installation. Derating will move them further:

179 A  ×  0.91 (40 °C)  ×  0.80 (2 circuits)  =  130 A

If the calculation clears at 50 mm², take it and save the 31%. If it does not, 70 mm² is the answer and the extra copper is doing real work rather than filling a gap in the series.

Conductor diameter

8.25 mm is solid wire, which does not exist at this size. At 50 mm²:

At 70 mm² the figures are 9.4, 11.0 and 13.1 mm — noticeably larger hardware for the same circuit, which is part of what the 31% actually costs. Lugs, glands and gland plates all move up. Take the overall diameter from the manufacturer's data for the construction you are buying. See conductor classes 1, 2, 5 and 6.

Where 1/0 is used

Service entrance conductors, sub-main feeders, larger motor circuits, welding cable, and battery interconnects in inverter and standby systems.

FAQ

What is 1/0 AWG in mm?

8.25 mm in diameter as solid wire, which is 324.9 mils. Stranded 1/0 measures up to 9.1 mm and flexible up to 11.0 mm at the equivalent metric size.

What is 1/0 AWG in mm²?

53.5 mm². The metric sizes either side are 50 mm² and 70 mm².

Should I use 50 mm² or 70 mm² for 1/0?

50 mm² is only 7% smaller and it meets the conductor resistance requirement. 70 mm² is 31% larger, the biggest round-up penalty in the range. Check the ampacity for your installation — 50 mm² XLPE covers 1/0 comfortably, while 50 mm² PVC sits slightly under it.

Is 1/0 the same as 50 mm²?

Not identical, but close. 50 mm² is 7% smaller and a 1/0 conductor meets its resistance limit, which makes it a defensible substitution where the ampacity works.

What does 0 AWG mean?

It is another way of writing 1/0, the first size above 1 AWG. The series continues 1/0, 2/0, 3/0, 4/0, also written 0, 00, 000, 0000.

How many amps is 1/0 copper?

125 A at 60 °C, 150 A at 75 °C, 170 A at 90 °C, before derating for ambient temperature and conductor grouping.

Reference

Convert any other size with the AWG to mm² converter.