1 bar is equal to 100 kPa. The use of bar should be strictly restricted in the field of fluid pressure.

Pressure unit based on CGS system (symbol dyn/cm^{2}). 1 dyne/square centimeter is expressed as 1 dyne force exerted on 1 square centimeter area.
1 dyn/cm^{2} = 0.1 Pa.

The pressure measured by a gauge is often the pressure difference between a system and the surrounding atmosphere. When the pressure difference is negative, the gauge pressure is also called vacuum or degree of vacuum.

Pressure is expressed as force per unit area. p = F/S, where the unit of pressure
is pascal (symbol Pa), SI unit for pressure, a special name for one newton per square
metre (N/m^{2}) after French scientist and philosopher Blaise Pascal (1623
- 1662).

The standard atmosphere varies in history for several times. The 10th Conférence Générale des Poids et Mesures (CGPM) (General Conference on Weights and Measures) in 1954 adopted the defintion of standard atmosphere (symbol atm) for general use as 1 standard atmosphere equals 1013250 dynes per square centimetre, i.e., 101325 newtons per square metre.

A technical atmosphere (symbol at) is a non-SI unit of pressure equal to 1 kilogram-force per square centimeter, i.e. 98.0665 kilopascals (kPa).

torr (symbol Torr) is a non-SI unit for pressure defined as 1/760 atm exactly. It is named after Evangelista Torricelli (1608 – 1647), an Italian physicist and mathematician is . With the standard atomasphere is defined as 101325 pascal exactly by CGPM, 1 torr is 101325/760 pascal.

The unit for pressure based on foot, pound and second. It is expressed as the pound
force per square inch area (symbol lbf/in^{2} or psi). 1 lbf/in^{2} = 6894.7573 Pa.