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Recommendation 1 of the 13th CCQM (2007)

On the possible redefinition of the mole and the kilogram

The Consultative Committee for Amount of Substance: Metrology in Chemistry (CCQM),


  • the recent proposals to redefine the mole in terms of a fixed value of the Avogadro constant and the kilogram in terms of a fixed value for either the Planck constant or the Avogadro constant,
  • the advantages that such redefinitions would bring to the scientific community through the significant reduction in the uncertainties of the values of many fundamental constants,
  • that the adoption of a fixed value for the Avogadro constant would have further benefits for the scientific community,

noting the existing discrepancy of about 1 part in 106 between the value of the Planck constant arising from the watt balance and x-ray crystal density/molar mass measurements,

recommends that

  • any decision on redefining the kilogram be deferred until the discrepancy between results from watt balance and x-ray crystal density/molar mass measurements has been resolved,
  • at that time, full consideration be given to redefining the kilogram and the mole by fixing the value of the Avogadro constant, and to the interests of the chemical measurement community,
  • any new definition of the kilogram and the mole should be straightforward to explain to the scientific community and understandable by the general public,
  • laboratories and organizations in communication with the CCQM, should consult widely within their communities to ensure the universal acceptance of the proposed definitions and their implementations.

DOI : 10.59161/CCQM2007REC1E

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