Standard wire gauge

Although its use has significantly declined, SWG sizes are still used for measuring the thickness of guitar strings and certain types of electrical wire.

In modern applications, wire size is more commonly measured in terms of cross-sectional area, expressed in square millimeters, particularly for electrical installation cables.

The current British Standard for metallic materials, including wires and sheets, is BS 6722:1986, which exclusively uses metric measurements.

SWG is not to be confused with American wire gauge, which has a similar but not interchangeable numbering scheme.

Because the weight per unit length is related to the cross sectional area, and therefore to the square of the diameter, the diameter diminishes by approximately 10.6%: However, the system is piecewise linear, only approximating the exponential curve loosely.