Resolution 6 of the 11th CGPM

Definition of the metre

The 11th Conférence Générale des Poids et Mesures (CGPM),


  • that the international Prototype does not define the metre with an accuracy adequate for the present needs of metrology,
  • that it is moreover desirable to adopt a natural and indestructible standard,


  1. The metre is the length equal to 1 650 763,73 wavelengths in vacuum of the radiation corresponding to the transition between the levels 2p10 and 5d5 of the krypton 86 atom.
  2. The definition of the metre in force since 1889, based on the international Prototype of platinum-iridium, is abrogated.
  3. The international Prototype of the metre sanctioned by the 1st CGPM in 1889 shall be kept at the BIPM under the conditions specified in 1889.

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


This definition was abrogated in 1983 by the 17th CGPM (Resolution 1).

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