The primary role of the Mass Department is to provide traceability to the international prototype of the kilogram. We do this by maintaining a number of prototypes and other standards in Pt/Ir. A subset of these is used as working standards to calibrate national prototypes upon request. The remainder are used for quality control. The combined standard uncertainty currently assigned to the calibration of a national prototype is typically 0.007 mg.

The BIPM offers a calibration service for 1 kg standards in stainless steel. This service is available free of charge to NMIs of Member States of the Metre Convention. The volume of the standard will be determined by hydrostatic weighing at the BIPM if this parameter is unknown (typical combined standard uncertainty obtained at the BIPM is 0.4 mm³ at 21.7 °C). However, the volumetric thermal expansion near room temperature must be supplied by the NMI or the manufacturer of the standard. If not already in our database, the BIPM will determine the location of the centre of gravity of the standard. The combined standard uncertainty currently assigned to the calibration of a 1 kg standard in stainless steel is typically 0.015 mg.