SI Update: The ronna, quetta, ronto and quecto

Government representatives worldwide met at the 27th General Conference of Weights and Measures on 15 to 18 November 2022 voted to add four new prefixes , the ronna, quetta, ronto and quecto to expand the range of prefixes used with the International System of Units (SI). See Table 1 for the full range of the SI prefixes with effective 18 November 2022. An update of the SI Brochure will be published at the International Bureau of Weights and Measures (BIPM) website ( in due course.

The SI prefixes are an essential part of the SI ensuring unified communication of measurements for effective interpretation across disciplines among the users. They allow us to extend the use of the SI as widely as possible when measurements get very large or very small by attaching to the SI base units or SI derived units to form new multiples or sub-multiples of these units. For instance, 0.000 000 001 m becomes 1 nm (nanometre), and 1 000 000 000 W becomes 1 GW (gigawatt).

The change was largely driven by the growing requirements of data science and digital storage, which is already using prefixes at the top of the existing range. The prefixes for very small numbers are useful for quantum science and particle physics.

Table 1 SI Prefixes
SI prefixes are used to form decimal multiples and submultiples of SI units. The grouping formed by a prefix symbol attached to a unit symbol constitutes a new inseparable unit symbol.
SI Prefix Table