relativ density

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The relative density  d , also specific density , describes the quotient of two densities as the quantity of the dimension number .



  • the density ρ of a substance under consideration (defined in DIN 1306 as mass per volume ).

The symbol  ρ 0 stands for the reference variable to which the density under consideration is related ( see following chapter ):

  • either the density of a normal state of the substance under consideration
  • or (more often) the reference density of an upholstery fabric .

Use and reference values

With solids

In mineralogy and engineering , density data are mostly based on the density of pure water in the normal state at 3.98 ° C. Use is useful when a material - e.g. B. as a result of different temperatures - exists in different structures, e.g. B. with larger or smaller porosity .

With liquids

The relative density is the ratio of the mass of a certain volume of a liquid at temperature T1 to the mass of the same volume of water at temperature T2:

  • A common relative density is , this describes the density of a liquid at 20 ° C in (z. B. 2 g / cm³) in relation to the density of water at 20 ° C (approx. 1 g / cm³). The relative density would then be 2, so the liquid, at 20 ° C, is twice as dense as water at 20 ° C.
  • Another example is , this describes the density of a liquid at 20 ° C in relation to the density of water at 4 ° C, more precisely at 3.98 ° C.

With gases

In the case of gases , the relative density is usually used to represent the “gravity ratio” to dry air . See DIN 1871 (May 1999), in which the relative density of a gas is defined as the quotient of the density of a gas and the density of dry air at the same pressure and temperature :

  • a gas with a relative density <1.0 is lighter than air, so it rises upwards: e.g. B. natural gas with .
  • a gas with a relative density> 1.0 is heavier than air and thus falls downwards: e.g. B. LPG or propane with .

Other common standard reference densities ( normals ) for gases are the densities of dry air:


  • DIN 1306 density; Terms, information
  • DIN 1871 Gaseous fuels and other gases - density and other volumetric quantities
  • Bergmann, Schaefer: Textbook of Experimental Physics , Volume 1, 11th Edition

Individual evidence

  1. European Pharmacopoeia , Deutscher Apotheker Verlag Stuttgart, 6th edition, 2008, pp. 33–34, ISBN 978-3-7692-3962-1 .
  2. The International pharmacopoeia, Volume 1 in the Google book search.