ISO 18852:2005 specifies a method for the determination of the nitrogen surface area (NSA) of carbon blacks and other rubber compounding ingredients, like silicas and zinc oxides, based on the Brunauer, Emmett and Teller (BET) theory of gas adsorption using a multipoint determination. This test method specifies the sample preparation and treatment, instrument calibration, required accuracy and precision of the experimental data, and calculation of the surface area results from the data obtained. Also given is a procedure for calculating the statistical thickness surface area (STSA), otherwise known as the external surface area. The test method specified uses an automatic volumetric static-vacuum apparatus, the surface area being calculated using the BET theory based on monolayer measurements.