On 18 November 2022 the 27th meeting of the General Conference on Weights and Measures (CGPM) approved the proposal to extend the range of prefixes for use with the International System of Units (SI). The prefixes for decimal multiples and submultiples of the SI units are, together with the definitions for the seven base units, an essential part of the SI. They allow an effective communication of technical and scientific information.

The prefixes for multiples of the units have been extended from 10²⁴, yotta, by adding ronna (symbol R) for 10²⁷ and quetta (symbol Q) for 10³⁰. These new prefixes are expected to find applications in the near future in the expression of quantities of digital information, which will require orders of magnitude well in excess of 10²⁴.

Prefixes for small submultiples of the units have also been added. These retain the “symmetry” of the large and small prefixes by introducing the ronto (symbol r) for 10^-27 and the quecto (symbol q) for 10^-30.

The authoritative document describing the International System of Units is the SI Brochure. It is available from the BIPM web site and has been updated accordingly.