[Fr.] A class of measuring instruments, whereof each has a specific name to indicate the kind of measurement for which it is to be used. Instruments of this nature are used for a variety of purposes, such as finding the capacity of a vessel (as in gauging a barrel), or in ascertaining the pressure of steam or the force of the wind or the amount of rainfall.

The standard gauge, or distance between the rails, in railways is 4 feet 81/2 inches. Broad gauge is 7 feet in England and 6 feet in the United States. Any gauge less than standard is called narrow gauge.