Use the free AWG to mm2 Converter below: your data never leaves your browser — all work happens on your device, and nothing is uploaded to any server.
What AWG means, in plain words
Wire size in North America is usually given in AWG, the American Wire Gauge system. It is a numbering system where a smaller number means a thicker wire, which surprises almost everyone the first time they meet it. A 14 AWG wire is thin and suits a normal lighting circuit, while a 4 AWG wire is thick, heavy and built for a much larger load. The scale even runs past zero into 1/0, 2/0 and 4/0 for the thickest cables, and those are read as one-aught, two-aught and four-aught.
The rest of the world mostly buys cable by cross-section in square millimetres, written mm². That number is the area of the copper or aluminium inside the wire, and it is the number that decides how much current the wire can carry and how much voltage it loses along the way. When you shop online, read a foreign wiring diagram, or follow a tutorial from another country, you often get one system and need the other. This converter translates between them in both directions, so a gauge number becomes a size in mm² and a size in mm² becomes the nearest AWG gauge.
How the conversion is calculated
The AWG system is built on a strict geometric rule. Each step of three gauge numbers halves or doubles the cross-section, and each single step changes the diameter by a fixed ratio of about 1.1229. From that rule comes the diameter formula used by this tool: diameter in millimetres equals 0.127 times 92 raised to the power of 36 minus the gauge, divided by 39. Once the diameter is known, the cross-section follows from the area of a circle, pi times diameter squared divided by four.
A worked example
Suppose a tutorial from the United States tells you to use 12 AWG wire for a circuit, but your local shop sells cable marked 4 mm². Enter 12 AWG and the tool shows about 3.31 mm², so 4 mm² is the next size up and a safe replacement in terms of copper area, though you must still check the local rating for your installation. Going the other way, suppose a European diagram calls for 2.5 mm² and you only have American stock. Enter 2.5 mm² and the tool returns 14 AWG as the nearest gauge, with a note that 14 AWG is actually about 2.08 mm², slightly smaller, so 12 AWG is the safer pick when the load is near the limit.
A second example shows why the direction matters. A thick 4/0 cable measures about 107 mm², which is an enormous conductor used for service entrances and large feeders, not for a bedroom socket. If you ever see a number like that on a plan and it does not match the job in front of you, stop and recheck: a misplaced decimal or a confused gauge is one of the most common and most expensive wiring mistakes, and it is exactly the kind of error a quick conversion check catches before any cable is cut.
Common mistakes when converting wire size
The first mistake is reading the scale backwards and assuming a bigger AWG number means a bigger wire. It is the opposite, and the error leads people to buy wire far too thin for the load, which overheats. The second mistake is comparing diameters instead of cross-sections. Two wires can look similar in diameter yet differ enough in area to matter, especially with stranded cable where insulation and air gaps inflate the outside measurement. Always compare mm², not the outside diameter of the finished cable.
Frequently asked questions
Is 12 AWG the same as 4 mm²? No, but it is close in practice. 12 AWG is 3.31 mm², so 4 mm² is the next standard metric size up and is commonly used as its replacement. Is a lower AWG number always better? A thicker wire carries more current and loses less voltage, but it costs more, is harder to bend and may not fit the terminals or the conduit, so bigger is not automatically better for every job. Can I use this converter for aluminium wire? The gauge-to-area conversion is the same for copper and aluminium, because it describes geometry, not material. The safe current is different, though, so check the ampacity estimator for the material you actually plan to use.
Safety first: an estimate, not a code approval
Every electrical tool on this page is an educational estimator only. It is never professional advice and never a substitute for a licensed electrician. Electrical codes differ by country, region and building type, and they change over time. A result that looks fine here can still fail a local inspection, and a result that looks tight here can still be acceptable under a rule this simple calculator does not model, such as temperature correction, grouping, or a special location rule. Before you buy cable, cut a wall, or touch a panel, check your local electrical code and talk to a licensed electrician. Breaker, conduit and box-fill results are estimates, not code-compliance guarantees. If you are unsure about any part of a job, stop and ask a professional. Electricity can injure or kill, and no free online calculator changes that fact.