Sizes of cables and wires

The cable cross-section is a surface measurement (in mm²) and the cable diameter is a length measurement (in mm).

The cross-section of a cable is defined by the front surface of the cut wire material. Only the conductive components are taken into account, insulation material is not included. For multi-stranded or fine-stranded cables (wires), the front surfaces of the individual fine strands are added together. There is some “space” in between, for example, a fine-stranded cable has a larger outer diameter than a solid cable with the same cross-section. In Europe, the cross-section is usually given in mm².
The cross-section of a cable required for the respective application depends largely on the current which is required: the more current is to flow through the cable, the larger the cable cross-section. The cable length must also be taken into account, and the type of installation and the ambient temperature also play a role, as these components directly influence the current that a cable can transmit. A cable with a large cross-section can carry more current and has a lower resistance.

The cable diameter (ø) in mm determines the size or the outside diameter of a cable. The maximum diameter is determined, measured on the outer insulation.

We are often asked: When are the dimensions cross-section in mm² and diameter in mm used for cables and wires? Is there a clear distinction here? Country-specific customs prevail here: In Europe, for example, the cable cross-section is usually given in mm². However, in Europe, too, in electronics, for cables that are usually small, the cable diameter is usually given in mm. In principle, it can be assumed that for cables with a cross-section of less than 0.5 mm², only the diameter is often given.

In the American economic area, however, cable sizes are usually given in AWG numbers, which differ from the nominal sizes common in Europe. The nominal size AWG stands for American Wire Gauge. The AWG system is based on the manufacturing process for wires. In Germany, Europe and many other parts of the world, the cross-sections of cables are given in metric mm². Since AWG is calculated differently, a small AWG value defines a large cross-section. The larger the AWG number, the finer the wire.

Inevitably, there are large differences in the AWG specifications between solid and flexible stranded conductors. And AWG cross-sections do not match the metric cross-sections common in Europe, which is why the AWG values we specify can only be described as approximate. In the converted real metric value, they are usually slightly lower than the mm² we specify.

WG sizes refer to solid wires. The diameter of twisted wires can exceed the diameter of solid wires by up to 20%.

AWG Metic Comparison Table: Conversion of AWG into the units of cable cross-section and cable diameter

You might also be interested in: "Conductor classes for cables and wires"
To the author Johannes Wienecke