Measurement

Gauge (instrument), any of a variety of measuring instruments
Gauge (firearms)
Wire gauge, a measure of the size of a wire
- American wire gauge, a common measure of nonferrous wire diameter, especially electrical
- Birmingham gauge, a measure of ferrous wire and hypodermic needle diameter
- Jewelry wire gauge, the size of wire used in jewelry making
Sheet metal gauge, thickness of metal in sheet form
Film gauge, a physical property of film stock which defines its size
The size of objects used in stretching (body piercing), especially earrings
Gauge block, a metal or ceramic block of precisely known dimension, used in measuring
Sight glass, also known as a water gauge, for measuring liquid level heights in storage tanks and pressure vessels
Boost gauge, a gauge used in conjunction with turbo-super-chargers
Pressure gauge or vacuum gauge, see pressure measurement
Gauge pressure, pressure above ambient pressure
Stream gauge, for measuring height and discharge of a river or stream
Air core gauge, a type of rotary actuator often used in automotive instruments
Gauger, one who gauges or measures, typically dutiable commodities, such as wine, landed from ships at docks

Sizes

Track gauge, the distance between the two rails forming a railway track
Loading gauge, the maximum width and height of vehicles (engines, loaded wagons, etc.).
Structure gauge, the minimum size of bridges, tunnels, platforms, etc.
Axle load, the weight that an axle exerts on track
Variable gauge, system to allow railway vehicles to travel across a break of gauge

Gauge (knitting), the number of stitches in a given length
Gauge (actress), American pornographic actress
Gauge (band), post-hardcore band from Chicago, Illinois, USA
Gauge, Inc., a manufacturer of microphones and audio accessories
Change of gauge (aviation), when an aircraft type changes at a stopping point of a direct flight
Gauge (software), cross-platform test automation tool