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The standard atmosphere (symbol: atm) is a unit of pressure defined as Pa. It is sometimes used as a reference pressure or standard pressure. It is approximately equal to Earth's average atmospheric pressure at sea level.
History
The standard atmosphere was originally defined as the pressure exerted by a 760 mm column of mercury at and standard gravity (g<sub>n</sub> = ). It was used as a reference condition for physical and chemical properties, and the definition of the centigrade temperature scale set 100 °C as the boiling point of water at this pressure. In 1954, the 10th General Conference on Weights and Measures (CGPM) adopted standard atmosphere for general use and affirmed its definition of being precisely equal to dynes per square centimetre ()<!-- -->. This defined pressure in a way that is independent of the properties of any particular substance. In addition, the CGPM noted that there had been some misapprehension that the previous definition (from the 9th CGPM) "led some physicists to believe that this definition of the standard atmosphere was valid only for accurate work in thermometry."
Pressure units and equivalencies
A pressure of 1 atm can also be stated as:
:≈ kgf/cm<sup>2</sup>
:≈ m H<sub>2</sub>O
:≈ mmHg
:
:≈ inHg or technical atmospheres (at).
See also
- International Standard Atmosphere