Standard wire gauge

The British Standard Wire Gauge, often referred to as the Standard Wire Gauge or simply SWG, is a unit used to denote wire gauge (size) as defined by BS 3737:1964, a standard that has since been withdrawn. It is also known as the Imperial Wire Gauge or British Standard 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.