4/0 AWG in mm: Diameter, mm2 & Termination Size

4/0 AWG measures 11.684 mm across. Its cross-section is 107.2 mm², or 211,600 circular mils.

This is the largest gauge in the system. Above it the numbering stops and conductors are named by their circular mil area instead — 250 kcmil and upward. See kcmil to mm².

The metric choice is unusually balanced

Most gauges give you one sensible option. 4/0 gives you two:

11% down against 12% up. Nowhere else in the range are the two options this evenly matched.

And the resistance test points down rather than up. A 4/0 conductor runs 0.161 Ω/km, which clears the 95 mm² limit of 0.193 comfortably and misses the 120 mm² limit of 0.153 by about 5%.

So 95 mm² is the defensible match on the number that gets tested, and 120 mm² is margin. That reverses the usual advice, and it is worth 12% of the copper on a conductor this size.

Check it against the ampacity and volt-drop calculation before committing. But at feeder scale the difference between 95 and 120 mm² is real money, and the resistance requirement does not force you upward.

Ampacity

4/0 copper carries 195 A at 60 °C, 230 A at 75 °C, and 260 A at 90 °C, for not more than three current-carrying conductors at 30 °C ambient. For comparison, 120 mm² PVC with three loaded conductors clipped direct at 30 °C is rated 259 A, and 95 mm² is 223 A.

At this size the terminal rating almost always decides which column you may use. Equipment terminals rated 75 °C mean you take 230 A even if the cable insulation is rated 90 °C. Check what is stamped in the enclosure at both ends before reaching for 260 A.

Derating still applies on top. 120 mm² PVC in a 40 °C switchroom with two circuits together:

259 A  ×  0.87 (40 °C)  ×  0.80 (2 circuits)  =  180 A

That is a 30% reduction, and at 4/0 sizes it is often the difference between one cable and two in parallel.

The number that actually causes problems

Not the ampacity. The diameter.

11.684 mm is the solid conductor figure, and nothing at this size is solid. Real 4/0 is stranded, and the metric maximums at 120 mm² are:

17.0 mm against 11.684 mm is a 45% difference. That is not one lug size, it is several.

Compression lugs, cable glands and gland plates at this scale are ordered ahead of the cable and often have long lead times. Sizing them off the conversion table figure and discovering the drum is flexible class 5 means hardware that physically will not accept the conductor, on a job where the cable is already on site.

Take the overall conductor diameter from the manufacturer's data sheet for the specific construction. See conductor classes 1, 2, 5 and 6.

Where 4/0 is used

Main service conductors, large sub-main feeders, transformer and generator tails, motor circuits on bigger machines, and main earthing conductors on large services. It is also the practical upper limit for a single conductor that two people can pull by hand. Above 4/0 the work changes — winches, cable rollers, and usually parallel runs rather than one larger conductor.

FAQ

What is 4/0 AWG in mm?

11.684 mm in diameter as solid wire, which is 460.0 mils. Stranded 4/0 measures up to 14.5 mm and flexible up to 17.0 mm at the equivalent metric size.

What is 4/0 AWG in mm²?

107.2 mm². The metric standard's own conversion list rounds this to 107. The two sizes either side are 95 mm² and 120 mm².

Should I use 95 mm² or 120 mm² for 4/0?

95 mm² is 11% smaller and meets the conductor resistance requirement, which makes it defensible. 120 mm² is 12% larger and removes any argument. Unusually for this site, the resistance test does not force you upward — run the ampacity and volt-drop numbers and decide.

How many amps is 4/0 copper?

195 A at 60 °C, 230 A at 75 °C, 260 A at 90 °C, before derating. The terminal rating of the equipment usually limits which figure you may use.

Why is it called 4/0?

The gauge series runs out of numbers at 1 AWG, so larger sizes continue as 1/0, 2/0, 3/0, 4/0 — spoken "one aught" through "four aught." 4/0 is also written 0000. See how the AWG system works.

What comes after 4/0?

250 kcmil. Above 4/0 conductors are named by their circular mil area in thousands rather than by gauge number.

Reference

Convert any other size with the AWG to mm² converter, or continue to kcmil to mm² for larger conductors.