Metal wire is measured using gauging systems. American Wire Gauge (AWG) and Standard Wire Gauge (SWG) are two systems used to measure the gauge of wire. The gauge relates to the diameter or thickness of the wire. The use of these systems depends primarily on the geographical location of the wire manufacturer because they represent national standards for wire measurement. The type of metal being gauged is also a common factor as to which system is incorporated.
Standard Wire Gauge
Also known as Imperial Wire Gauge (IWG), the British Standard Wire Gauge (SWG) is the gauging measurement system incorporated in the UK. The basis of the SWG is measurement by the millimetre. The metric system is the standard for measurements in Britain where the SWG was created.
American Wire Gauge
The AWG is the American standard for the measurement of wire. Because the English system is the basis of measurement in the United States, the AWG system is measured based on inches. The AWG is also referred to as the Brown & Sharpe measurement system---named after the company that devised the system.
Brown & Sharpe
Brown & Sharpe (B & S) is an American company that has been involved in design of measurement systems and tools for more than 150 years. This company was once an independent entity, but is currently a subsidiary of Hexagon Metrology, Inc. The AWG system is often referred to as "B & S" as recognition of its creation of the system.
AWG and SWG have more differences than simply the fact that the measurements are based on standard vs. metric systems. When listed together in a conversion chart, the numbers are listed by number and the range goes to 56, although SWG stops at 51. SWG is normally used to measure the thickness of wire consisting of iron-based metals, while AWG is typically used to gauge precious metals.