Physical atmosphere [atm]: a unit of pressure equal to about 101,325 Pa (pascals) and corresponds to atmospheric pressure at sea level.

Technical atmosphere [at]: a unit of pressure equal to 1 kgf/cm², which is about 0.98 atm or 98 kPa.

Millibars [mbar]: a unit of pressure equal to 1/1000 bar, or 100 Pa.

Bars [bar]: a unit of pressure equal to 100 kPa. 1 bar is defined as the pressure exerted by a column of liquid with a density of 1 kg/m³ at a height of 10 meters under standard gravity.

Pascals [Pa]: the basic unit of pressure in the SI system, corresponding to a force of one newton acting on an area of one square meter.

Pounds per square inch [psi]: a unit of pressure equal to 1 pound-force per square inch, or about 6.89 kPa.

Torr [tor]: a unit of pressure equal to 1 mmHg, i.e., the pressure exerted by a column of mercury 1 mm high.

Meters of water column [msw]: a unit of pressure equal to the pressure exerted by a column of water 1 meter high, or about 9.81 kPa.

Millimeters of mercury [mmHg]: a unit of pressure equal to the pressure exerted by a column of mercury 1 millimeter high, mainly used in medicine.