Gauge, when applied to sheet metal, is used to determine the thickness of a single piece of sheet metal, with lower numerical values indicative of increasing levels of thickness. There are a number of standard gauge measurements in use, each with slightly different standard thickness.
Gauge, when used to measure the thickness of sheet metal, is also sometimes written as "gage," although the pronunciation remains the same.
There are two standard gauges used in the United States. The first is the Manufacturers' Standard Gage. This particular standard measurement is used mainly to provide the standard thickness ratings for a number of types of steel, including galvanized, standard and stainless steel.
The second standard is American Wire Gage, alternatively known as the Brown and Sharpe Gage. This measurement is used for a variety of non-ferrous metals such as aluminum, copper and brass.
Despite being a non-ferrous metal, zinc has its own standard gauge which differs from almost all others. A zinc gauge is measured in the opposite way to the metal gauges, in that the higher the number the thicker the sheet.
The standard sheet metal gauge in the U.K. is the Birmingham Gage. This gauge is used for almost all metals, encompassing a wide variety of different products.