Auto Cable Sizes in Australia: B&S, AWG and mm2 Explained

Auto cable sizes in Australia are quoted three ways at once. A parts store shelf might have 3mm and 6mm auto cable, an 8 B&S battery lead, and an overseas fridge manual asking for 10 AWG or 6mm2. They all describe copper, but they are not the same scale, and mixing them up is how people end up with a feed carrying about a quarter less copper than they intended.

This guide explains what each label means, gives the real copper area for the common Australian sizes, and shows which Solderstick connector colour suits each one.

Quick answer:

• Australian "mm" auto cable labels are not the copper area. 3mm auto is about 1.13mm2, 4mm about 1.8mm2, 5mm about 2.9mm2 and 6mm about 4.6mm2.
• B&S and AWG are the same numbering scale. 8 B&S is nominally 8 AWG (8.37mm2), though Australian 8 B&S auto cable is often closer to 7.7-7.9mm2.
• mm2 is the number that matters. When a manual asks for a size, convert it to mm2 and buy cable with at least that much copper.

Why auto cable sizes in Australia are confusing

The local "mm" labels are a trade naming system that has been around for decades. The number roughly tracks the overall size of the cable, but it is not the conductor diameter and it is definitely not the cross-sectional area. A 3mm auto cable from a major Australian maker has 14 strands of 0.32mm wire, which adds up to about 1.13mm2 of copper.

Meanwhile, heavy cable is sold in B&S, imported gear is specified in AWG, and European and Asian gear uses metric mm2. Three scales, one shelf.

The fix is simple: convert everything to mm2 before you compare. Most Australian cable makers print or list the mm2 figure, even when the product name uses the old label.

Auto cable sizes chart: label, mm2 and AWG

These figures come from Australian makers' published single core data. Exact areas vary slightly between brands and strand counts, so treat them as typical.

The ratings are one maker's figures for a single core in free air at 30 degrees C. They are a ceiling, not a design target, and they drop for twin core, bundled looms and hot engine bays. Size for voltage drop as well; our 12V wire gauge guide has a run length table.

B&S vs AWG: same scale, slightly different cable

B&S stands for Brown and Sharpe, who devised the scale that became American Wire Gauge. The numbers line up exactly: 6 B&S is 6 AWG, 2 B&S is 2 AWG. Lower numbers mean thicker cable, and every three sizes roughly doubles the copper.

The catch is that the AWG figures are for an ideal conductor, while real stranded cable is built from a whole number of strands. Australian 8 B&S auto cable is commonly listed at 7.71 or 7.91mm2, a little under the 8.37mm2 of true 8 AWG. 6 B&S lands at about 13.5mm2, very close to 6 AWG at 13.3mm2. If an installation manual calls for 8 AWG and the run is long, 6 B&S removes any doubt.

True AWG areas for reference

Metric mm2 cable and Australian auto cable

Metric cable is sold by its actual area in standard steps: 0.5, 0.75, 1.0, 1.5, 2.5, 4, 6, 10, 16, 25 and 35mm2. Those numbers mean what they say.

This is where the biggest mistake happens. A manual that asks for 6mm2 is asking for about 30 percent more copper than Australian 6mm auto cable. A manual that asks for 4mm2 wants more than 4mm auto (1.8mm2) and more than 5mm auto (2.9mm2); 6mm auto (4.59mm2) is the first local label that meets it.

A quick rule: when converting a metric spec to Australian auto cable sizes, find the local cable whose real mm2 is equal to or larger than the spec, never the one with the matching label.

Reading auto cable current ratings properly

Australian cable ratings are usually quoted for a single core at 30 degrees C. Real installs are rarely that kind:

• Twin core and twin sheath cable runs warmer, so it is rated lower. One Australian supplier gives an 8 B&S example dropping from 74A single core to 59A as twin core.
• Bundled looms share heat. Makers publish derating factors for bundles; some cite the Japanese JASO D609 method.
• Engine bays are hot. Expect less than the 30 degree figure near the exhaust or turbo.

Then check voltage drop. On a 12V system a 10 percent loss is 1.2V, enough to make a fridge cut out or a DC-DC charger throttle back. Over a long run, voltage drop will usually push you to a bigger size than the current rating alone.

Single core, twin core and twin sheath cable

The same auto cable sizes are sold in several constructions. Single core is one insulated conductor. It is the most flexible to route and has the highest rating for its size.

Twin core puts two insulated conductors side by side, often red and black, for a positive and negative pair. Twin sheath adds an outer jacket over both, which is tougher against chafe and UV and is the usual choice for runs under the vehicle or out to a trailer or caravan.

Whatever you choose, stick with multi-strand automotive cable. Household 230/240V cable uses fewer, thicker strands and does not belong in a vehicle loom.

Matching auto cable sizes to Solderstick connectors

Solderstick connectors are sized by colour. Here is how the common Australian auto cable sizes line up with the listed ranges.

For a dry fit, slide the stripped ends into the tube: the bare copper should sit under the solder ring and the sealing rings should sit over the insulation. Contact us before ordering if you are unsure. Our connector colour chart goes into more detail, and how to use Solderstick connectors covers the heating step.

Anything heavier than 6mm2, including battery, winch and starter cables, needs crimped or soldered lugs rather than a splice connector. Size the cable and fuse for the load first: a good join does not make undersized cable safe.

Which should you use?

• If you're wiring a relay trigger, switch light or trailer lamp tail, use 0.5-1.0mm2 cable and red connectors.
• If you're running a single light, USB socket or radio over a short run, use 4mm auto (about 1.8mm2) and blue connectors.
• If you're feeding a fridge, light bar or accessory socket, use 6mm auto (about 4.6mm2) or heavier and yellow connectors, after checking voltage drop.
• If you're wiring a DC-DC charger or dual battery link, use 8 B&S or 6 B&S as the charger manual specifies, with crimped lugs. See our dual battery wiring guide.
• If a manual gives a metric mm2 size, buy the Australian cable whose real mm2 meets or beats it.

Frequently asked questions

What does 3mm auto cable mean?

It is a trade label, not a measurement of copper. Australian 3mm auto cable has about 1.13mm2 of copper, roughly 17 AWG, and is typically rated around 20A as a single core at 30 degrees C.

Is 6mm auto cable the same as 6mm2?

No. 6mm auto cable is about 4.6mm2 of copper. If a manual asks for 6mm2, you need more copper than 6mm auto provides, so step up to 8 B&S.

Is 8 B&S the same as 8 AWG?

Yes, they are the same scale. True 8 AWG is 8.37mm2, while Australian 8 B&S auto cable is often listed at 7.7-7.9mm2 because of its strand count.

What size is 6 B&S in mm2?

About 13.3-13.5mm2. It is a common size for DC-DC charger runs to a canopy or caravan and for short heavy-duty feeds.

Can I use household electrical cable in my car?

No. Household cable has fewer, thicker strands that crack under vibration and is not designed for vehicle use. Fixed 230/240V mains wiring in Australia must be done by a licensed electrician.

What auto cable size do I need for 20 amps?

For a short run, 4mm or 5mm auto cable is within its rating, but voltage drop usually decides. Over more than about 2 metres one way, 6mm auto or 8 B&S keeps the drop near 3 percent.

What to use

Once you have the auto cable sizes sorted, an assorted kit covers every connector colour for a mixed loom. The 100PCS kit has 25 white, 35 red, 30 blue and 10 yellow, and the 50PCS kit suits a glovebox spares bag. For bigger jobs, see the 250PCS kit.

If you mostly run one cable size, the bulk 100-pack bags come in a single colour. For sealing lugs on 8 B&S and heavier cable, use adhesive-lined dual wall heat shrink. Free express shipping Australia wide, with orders by 1pm dispatched the same day.