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Pressure gauges are instruments used to measure positive pressures. Pressure, here, is the force acting on a particular surface, measured per area. The general units of measurement are pound forces per square inch (psig). A car tire exerts about 32 psig, while an extremely high-pressure operation will exert more than 5,000 psig. There are a number of other gages for measuring non-standard pressures. Vacuum gages measure negative pressures (those below atmospheric pressure). Differential gages are industrial instruments that measure the difference between two pressure input connections. Compound gages are designed to indicate both positive and negative pressures.

Pressure gages rank among the most important instruments in industrial applications. They also rank among the most frequently misused and poorly maintained measurement devices. In many cases, this is because a pressure gage was not actually required and added only as a force of habit. Unfortunately, this may lead to laxity about maintaining essential pressure gages. Properly maintained and operated gages, however, provide valuable manufacturing tools.

Pressure gages work in a variety of ways. Traditional Bourdon gages use pinions, links and pivots to process pressure and translate it to the display instrumentation. Its sensitive parts, however, are often subject to environmental factors, and prone to eventual failure. A standard modern pressure gauge consists of a ring, glass lens, lens gaskets, pointer, dial, sensor and casing. In many new gauges, the housing is filled with specialized oil. This oil helps reduce pointer jumping and prevents water condensation within the gage, thereby adding to its working life. These are called filled gages. Dry gages contain only the gauge mechanism.

In industrial applications, pressure gauges often work in tandem with a shutoff valve. At a certain given pressure, the gage will trigger the shutoff valve. This will reduce pressure, which will then cause the shutoff valve to release. A variety of materials are used in pressure gages. Stainless steel is extremely reliable and used in corrosive applications. Brass is also used, as it performs well in moist environments. Even thermoplastic gauges have found use.