Gauge

Gauge is an engineering term referring to a measure of width or thickness, or to devices used to make measurements (originally thickness or width). It can also be used as a verb to describe the act of taking a measurement, typically an estimate.

Gauge is most commonly used when referring to railways, where gauge referrs to the distance between the two rails of the roadbed (eg standard gauge, narrow gauge). The term is also used in the measurement of metal sheeting, where it refers to the thickness of the sheet. It is more rarely used to refer to the internal dimensions of a cannon.