ISO 1183-1:2004 specifies three methods for the determination of the density of non-cellular plastics in the form of void-free moulded or extruded objects, as well as powders, flakes and granules.
Method A: Immersion method, for solid plastics (except for powders) in void-free form.
Method B: Liquid pyknometer method, for particles, powders, flakes, granules or small pieces of finished parts.
Method C: Titration method, for plastics in any void-free form.
This part of ISO 1183 is applicable to pellets as long as they are void-free.