AWG to mm² Conversion Chart: Wire Size and Lug Selection

To convert AWG to mm², take the AWG gauge, work out the conductor diameter from the gauge progression, and calculate the area from that diameter. AWG 10 is 5.26 mm², AWG 6 is 13.3 mm², AWG 2 is 33.6 mm², 1/0 AWG is 53.5 mm² and 4/0 AWG is 107 mm². When you then order metric cable or a metric lug, round up to the next standard cross-section — never down.

That last sentence is where most of the money is lost. The conversion itself is arithmetic. Deciding what to do with the answer is the part that determines whether a lug fits a cable and whether a joint runs cool for twenty years.

Where the two systems come from

AWG is a gauge number, not a measurement. The system is a geometric progression: each step of three gauges halves the area, which means each single step multiplies the area by about 1.26. A lower number is a thicker conductor, and the scale runs past zero into 1/0, 2/0, 3/0 and 4/0 — usually spoken as "one aught", "two aught" and so on. Above 4/0 the American system abandons gauge numbers and switches to thousands of circular mils, written kcmil or MCM.

Metric cable is the opposite idea. It is sold by nominal cross-sectional area in square millimetres, and the standard sizes are a fixed ladder: 0.5, 0.75, 1, 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185, 240, 300, 400, 500 and 630 mm². There is no size between 120 and 150.

So a drawing written in AWG almost never lands exactly on a metric size. That mismatch is the entire practical problem this page exists to solve.

The conversion, step by step

The diameter of an AWG conductor in millimetres is fixed by the definition of the gauge:

d (mm) = 0.127 × 92^{(36 − n) / 39}, where n is the AWG number, negative for the aught sizes (1/0 = 0, 2/0 = −1, 3/0 = −2, 4/0 = −3).

The cross-sectional area follows from the diameter in the ordinary way, area = π d² / 4. For kcmil, one kcmil is 0.5067 mm², so 250 kcmil is 126.7 mm².

You do not need to run the formula at the bench. Use the table below, which was calculated from it.

AWG to mm² conversion table

kcmil to mm²

Why the conversion does not give you an ampacity

This is the single most expensive misunderstanding in the whole topic. Two conductors with the same cross-section do not have the same current rating. Ampacity depends on the insulation temperature rating, the number of conductors bundled together, whether the run is in free air, in conduit, in a wall, in a tray, the ambient temperature of the site, and the installation standard the project is being inspected against.

The same 5.26 mm² of copper can be a 10 AWG conductor in one code and a 6 mm² conductor in another, with different permitted loading, because the two systems also differ in how they count insulation and how they derate for grouping. Converting the area tells you how much metal you have. It does not tell you what that metal is allowed to carry.

So do not take a US ampacity figure, convert the gauge to mm², and apply the result to a metric installation. Work in one system for sizing and use the conversion only where the two systems physically meet: at the lug, the terminal block and the joint.

Where the conversion actually decides the purchase

The joint is the place where an AWG world and a metric world collide, and it is where the rounding rule earns its keep.

• The barrel, not the palm. A cable lug has two dimensions: the barrel that receives the conductor and the palm that bolts to the busbar. A conversion error almost always shows up in the barrel. A lug listed for 120 mm² will not accept a 250 kcmil conductor properly, because 250 kcmil is 126.7 mm² — the metric size is smaller than the conductor. The first metric size that is genuinely not smaller is 150 mm².
• Dual-range lugs remove the guesswork. A lug such as the TA-250 is specified as a range, 250 mcm down to 6, precisely so one part covers a band of American sizes without a table. Where a drawing is in AWG and the stock is chosen in ranges, order by the range.
• Material decides the joint, not the gauge. Aluminium conductor on a copper busbar needs a bimetallic transition, or the joint will corrode. The DTL-2 series is a copper-aluminium bimetal ring lug for exactly that transition; the DTL-2-35/2-70 is the same idea in a fixed 35 to 70 mm² format. Matching the metal matters more than matching the area to two decimal places.

Matching a lug to a converted size

Once the conductor is expressed in mm², the selection is mechanical rather than arithmetic:

1. Conductor material and class — copper or aluminium, stranded or flexible. A flexible class conductor needs a finer-strand barrel or a ferrule; a coarse stranded conductor does not.
2. Barrel size — must take the actual conductor, not the nominal one. If the conductor is 126.7 mm² and the lug is bored for 120 mm², the crimp will be hollow.
3. Palm and stud — hole diameter, hole spacing and the number of holes. Two-hole palms are used where the joint must resist vibration and rotation; single-hole palms where space is tight.
4. Plating and environment — tinned or silver-plated copper for humid or corrosive sites. The AWG series bell-end lug is a silver-plated copper terminal; the two-hole copper crimp lugs in the same range are supplied RoHS compliant.
5. Voltage context — a lug rated 600 V and a lug intended for 35 kV are different products even when the barrel geometry looks similar.

Terminal blocks and comb busbars

Panel wiring hits the same mismatch one size down. A DIN rail terminal block is rated by conductor range and by current, and a fork-type comb busbar distributes a shared feed across a row of blocks. In this range the comb busbar terminal block is rated for 100 A maximum continuous current, which is the number that limits the row — not the sum of the block ratings.

If a schedule mixes AWG and mm² across a single row, convert every entry to mm² first and check the row against the busbar rating, not against the largest block on the rail.

Selection checklist for a mixed-unit order

• Convert every conductor on the drawing to mm² and keep the original gauge in the description.
• Round up to the next standard size for cable and for lug barrels; never round down.
• State the conductor class, not only the area.
• State the stud size and hole spacing for the palm.
• State the metal on both sides of every joint and specify a bimetallic transition where they differ.
• Put the ambient and installation conditions in the enquiry, so the current rating is not guessed from the area alone.

Send the drawing as it is written. A manufacturer who builds both American and metric terminals will recognise the AWG numbers and confirm the metric equivalent, which is faster and safer than converting on the buyer's side and hoping the rounding went the right way.

Frequently asked questions

Is AWG 10 the same as 6 mm²?

No. AWG 10 is 5.26 mm², so the next metric size up is 6 mm². They are close but not equal, and the metric conductor carries slightly more copper. For a lug barrel, 6 mm² is the size that will accept an AWG 10 conductor properly; a 4 mm² lug will not.

How many mm² is 4/0 AWG?

4/0 AWG is 107.2 mm², with a conductor diameter of 11.684 mm. The next standard metric size up is 120 mm². Do not substitute 95 mm², which is smaller than the conductor it is meant to receive.

Is 250 kcmil the same as 120 mm²?

No. 250 kcmil is 126.7 mm². A 120 mm² lug is undersized for it. The first standard metric size that is not smaller than 250 kcmil is 150 mm².

Can I use the mm² figure to look up ampacity?

Only within the same standard. Ampacity comes from the insulation rating, the installation method, the ambient temperature and the derating rules of the code the installation is inspected against. A converted area is a physical dimension, not a current rating.