In science and engineering, a gauge is a device used to make measurements or to display certain dimensional information. A gauge can be described as "a device for measuring a physical quantity", for example "to determine thickness, gap in space, diameter of materials, or pressure of flow", or "a device that displays the measurement of a monitored system by the use of a needle or pointer that moves along a calibrated scale". There are many types of gauges, ranging from simple pieces of material against which sizes can be measured to complex pieces of machinery.
In general, a gauge is a measurement of a particular dimension or quality. For example, a gauge can refer to the distance between the rails of a railroad, the size of a shotgun barrels inner diameter, the thickness of a thin material such as sheet metal or plastic film, or the diameter of a slender object such as wire or a hypodermic needle. A gauge can also refer to an instrument for measuring a dimension or for testing mechanical accuracy, such as an instrument with a graduated scale or dial for measuring or indicating quantity.
In addition to these uses, the term "gauge" can also refer to a measure of the size of a wire, such as American wire gauge or Birmingham gauge. It can also refer to the thickness of metal in sheet form, the physical property of film stock which defines its size, or the size of objects used in stretching (body piercing), especially earrings. Finally, "gauge" can refer to the act of calculating an amount by using a measuring device or by one's own judgment, or to make a judgment about people's feelings.
