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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.

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