The SI Brochure is the reference document describing the International System of Units (SI), the only internationally recognized system of units. This new version of the brochure includes changes to the section on non-SI units and updates the presentation of explanatory notes throughout the publication.
Des changements pour clarifier les unités non-SI
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Version 2.01 of the 9th edition of the booklet included the new SI prefixes adapted by the CGPM. Then, in 2024, version 3.01 of the 9th edition was published, improving the description of angles and units of one. Version 3.02 was subsequently published in 2025, revising the value of the dalton and updating the list of binary prefixes.
Version 4.01 of the 9th edition has just been released; it now contains a revised description of the relationships between commonly used non-SI units and the SI.
Among the changes in the brochure:
Clarification of the presentation of non-SI units
Introduction of a more comprehensive list of non-SI units, along with their conversion factors to SI units
For the first time since the formalisation of the SI, the SI Brochure clearly states that non-SI units do not have any special status within the International System of Units (SI).
Downloadable SI brochure
The listed units are organised into four indicative categories:
Long-established units of time and angle
Historical names for decimal multiples and submultiples of SI unit
Internationally recognized units that are neither decimal multiples nor submultiples of SI units
Units used in specialised technical disciplines
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Cover of the 9th edition of the SI brochure
Version 4.01 of the 9th edition of the SI brochure is available for download on the BIPM website
