# Gases: Pressure

### Terms

Atmosphere  -  A unit of measurement defined as 101,325 Pascals. The typical pressure at sea level varies around one standard atmosphere (atm). Atmospheric pressure P can be calculated via the following equation:

 P = ghρ

Bar  -  A unit of measurement equivalent to 1×105 Pascals.
Barometer  -  A device used to measure atmospheric pressure.
Barometers.
mm Hg  -  A unit of pressure commonly used with the barometer. It corresponds to 1 torr and 1/760 atm at 0 o Celsius only.
Pascal  -  The SI unit of pressure. 1 Pascal = 1 N/m2 .
Pounds per Square Inch  -  A unit of pressure commonly used in the United States. 1 psi = 1 lb in-2 . 14.6960 psi corresponds to one atmosphere.
Pressure  -  Pressure = Force/Area. The standard atmospheric pressure is 101,325 Pascals.
Torr  -  A unit of pressure closely related to mm Hg, but more convenient and absolute. 1 Torr = 1 mm Hg at 0 o Celsius. 1 Torr always equals 1/760 atm, irrespective of the temperature.

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