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An amagat is a practical unit of number density. Although it can be applied to any substance at any conditions, it is defined as the number of ideal gas molecules per unit volume at 1 atm (= 101.325 kPa) and 0 °C (= 273.15 K).[1] It is named after Émile Amagat, who also has Amagat's law named after him. The abbreviated form of amagat is "amg". The abbreviation "Am" has also been used.[2]


Number density in amg, denoted here by , is defined as


where n0 = 1 amg = 2.686 7805×1025 m−3 = 44.615 036 mol/m3 is the Loschmidt constant.

In practice, number density of an ideal gas at pressure P and temperature T can be calculated as[3]


where T0 = 273.15 K and p0 = 101.325 kPa.


Number density of an ideal gas (such as air) at room temperature (20 °C) and 1 atm (101.325 kPa) is



  1. ^ Hirschfelder, Joseph O.; Curtiss, Charles F.; Bird, R. Byron (1967), Molecular Theory of Gases and Liquids (Corrected printing ed.), John Wiley & Sons, Inc. 
  2. ^ V. G. Teifel (1976). "Methane and ammonia abundance in the atmosphere of Saturn". Sov. Astron. Lett. 2 (6). 
  3. ^ In this formula, absolute units of pressure and temperature, relative to vacuum and absolute zero, must be used.