SWG, or Standard Wire Gauge, is a measurement system used to determine the diameter of electrical wires. It provides a standardized way to classify wire sizes, which is essential for ensuring compatibility and safety in electrical applications. The gauge number inversely relates to the wire's diameter; as the gauge number increases, the wire diameter decreases. The SWG system is commonly used in the United Kingdom and other countries for various types of wires, including those used in electrical engineering and crafting. Understanding SWG helps users select the appropriate wire for their specific needs, ensuring optimal performance and safety.