The following definition is given in DIN 1306 (June 1984): "The density r is the quotient from the mass m and volume V of a portion of material:

… A density specification is complete only when everything with a notable effect on its value is listed, e.g. chemical composition, state of aggregation, modification, pretreatment, temperature, pressure, moisture. … The relative density d is the ratio of the density r of a material or mixture to the reference density r₀ of a reference material under conditions which must be separately specified for both materials. The relative density is a variable ratio and has the dimension 1:

… The relative density must be used only for gases. …" With regards to sealing, density is used to determine the sealing pressure and to assess the leakage characteristics.