AWG is an acronym for "American Wire Gauge" (German translation: "Amerikanische Drahtlehre"). As you may have already concluded, this coding system originates from North America. It reflects a geometric sequence that was introduced in the middle of the 19th century by Joseph Rogers Brown for use in his tool-making company Brown & Sharpe.

The AWG standardized wire gauge system is used to plot diameters and cross-sections of electrical conductors made out of non-ferrous metals, applied to both wires and strands. The AWG graduation is based on the number of drawing steps required to produce a certain diameter. In order for the wire to arrive at the desired diameter, a fairly thick base wire (e.g. 0.8 mm) is drawn through the tapered mouth of a drawing die. Reducing the diameter only works very gradually, i.e. by means of several drawing steps, with the mouths that are used getting smaller and smaller until the final diameter is obtained.

The AWG system clearly defines the range 0000 (4/0) to 36, where all sizes in between adhere to a geometric sequence that comply with the following rule: the AWG figure is a function of the number of drawing steps resulting in ever-decreasing diameters. Even sizes below AWG36 follow the same pattern as they are derived from the size range initially covered.

The unit of the diameter is
in resp. mils = in * 1,000

Cross-sections above 4/0 are indicated in
cmils

The ratio between diameters and corresponding AWG sizes can be found in ASTM B 258-02:

Any diameter can be inferred from an AWG figure by making use of the above formula as follows:

Below you can see the inverse calculation (AWG from diameter):

As opposed to the usual way of calculating a circular area (single-wire cross-section in mm) according to the formula

the AWG system features a simplified calculation using d².

This leads to an AWG cross-section stated in
"circular mil area" cma = (d mils)².

Example:

AWG36 = 0.005 in = 5 mils

(5 mils)² = 25 cma

The AWG figure basically stands for a cross-section only. Therefore, any dimension relative to both single wires as well as strands is expressed as such an AWG figure.

Just to make matters more complicated, it is the construction of a strand that has a crucial impact on some of its major properties like flexibility, resistance, conductivity or tensile strength. This aspect has led to the inclusion of the construction whenever an AWG indication is applied. An AWG28 strand, for instance, may consist of seven AWG36 single wires. This is reflected by the designation "AWG28 7/36".

Practitioners have developed approximations for the quick calculation of strand sizes, which can be employed to a certain extent:

6 AWG steps down → diameter is doubled
6 AWG steps up → diameter is halved
3 AWG steps down → cross-section is doubled
3 AWG steps up → cross-section is halved

With telephony growing more and more widespread in the middle of the 19th century, the wire industry experienced an extraordinary technological boost. Industry and commerce were using completely different units of measurement at the time. Joseph Rogers Brown contributed to making the American Wire Gauge system the predominant measuring tool, which lead to an increased standardization in this field. This development has continued to influence the entire product range when it comes to wires made from non-ferrous metals.

Ongoing technological progress has caused some fundamental changes to the wire drawing process. Fixed definitions have partly been superseded by individual solutions. This has rendered the drawing process more flexible across the board, thus also facilitating the production of wires beyond the standard AWG sizes. In spite of AWG still being a common scaling factor for cable sizes, it is more and more replaced by the metric system.