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Other non-SI units not recommended for use
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Non-SI units accepted for use with the SI, and units based on fundamental constants
Other non-SI units not recommended for use

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SI brochure, Section 4.2

There are many more non-SI units, which are too numerous to list here, which are either of historical interest, or are still used but only in specialized fields (for example, the barrel of oil) or in particular countries (the inch, foot, and yard). The CIPM can see no case for continuing to use these units in modern scientific and technical work. However, it is clearly a matter of importance to be able to recall the relation of these units to the corresponding SI units, and this will continue to be true for many years. The CIPM has therefore decided to compile a list of the conversion factors to the SI for such units and to make this available on the BIPM website at

Note: For the official text, please refer to the PDF files available at:
  • (in English) and
  • (in French).