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Recommendation 1 of the 12th CCM (2010)

Considerations on a new definition of the kilogram

The Consultative Committee for Mass and Related Quantities (CCM)

recalling its previous Recommendation to the CIPM on the “Conditions for a new definition of the kilogram”, CCM G 1 (2005), and


  • further discussion at its 10th and 11th meetings held in 2007 and 2008,
  • recent progress in experimental determinations of the Planck and the Avogadro constants, and
  • other experimental progress allowing a mise en pratique for the realization and the dissemination of the new definition of the kilogram now to be prepared,

noting that watt balance experiments and the International Avogadro Coordination project represent two distinct routes to determining the Planck constant,


  • that the following conditions be met before the kilogram is redefined in terms of fundamental constants:
    1. at least three independent experiments, including work both from watt balance and from International Avogadro Coordination projects, yield values of the relevant constants with relative standard uncertainties not larger than 5 parts in 108. At least one of these results should have a relative standard uncertainty not larger than 2 parts in 108,
    2. for each of the relevant constants, values provided by the different experiments be consistent at the 95 % level of confidence,
    3. traceability of BIPM prototypes to the international prototype of the kilogram be confirmed,
  • that the CODATA recommended values be adopted for the relevant fundamental constants,
  • that the associated CODATA relative standard uncertainties be suitably considered when the initial uncertainty is assigned to the mass of the international prototype of the kilogram,
  • that a pool of reference standards be established at the BIPM to facilitate the dissemination of the new definition of the kilogram,
  • that the BIPM and a sufficient number of National Metrology Institutes continue to develop, operate or improve facilities or experiments that allow the realization of the kilogram to be maintained with a relative standard uncertainty not larger than 2 parts in 108.
  • that the uncertainty component arising from the practical realization of the unit be suitably taken into account.

DOI : 10.59161/CCM2010REC1E

The reader should note that the official version of this Resolution is the French text