Pressure (symbol: p or P) is the force applied perpendicular to the surface of an object per unit area over which that force is distributed.[1]:445 Gauge pressure (also spelled gage pressure)[lower-alpha 1] is the pressure relative to the ambient pressure.

Common symbols
p, P
SI unitpascal [Pa]
In SI base units1 N/m2, 1 kg/(m·s2), or 1 J/m3
Derivations from
other quantities
p = F / A
DimensionM L−1 T−2
Pressure as exerted by particle collisions inside a closed container

Various units are used to express pressure. Some of these derive from a unit of force divided by a unit of area; the SI unit of pressure, the pascal (Pa), for example, is one newton per square metre (N/m2); similarly, the pound-force per square inch (psi, symbol lbf/in2) is the traditional unit of pressure in the imperial and U.S. customary systems. Pressure may also be expressed in terms of standard atmospheric pressure; the atmosphere (atm) is equal to this pressure, and the torr is defined as 1760 of this. Manometric units such as the centimetre of water, millimetre of mercury, and inch of mercury are used to express pressures in terms of the height of column of a particular fluid in a manometer.

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