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The SI system now has four prefixes for numbers beyond the range covered by its previous list: ronna (R) means 1027, quetta (Q) means 1030, ronto (r) means 10−27, and quecto (q) means 10−30. The 27th General Conference on Weights and Measures (CGPM) adopted them on 18 November 2022.
What are the four new SI prefixes?
Each prefix represents a power of ten. Ronna and quetta scale a unit up; ronto and quecto scale it down.
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| Prefix | Symbol | Factor | Meaning when attached to a unit |
|---|---|---|---|
| ronna | R | 1027 | One billion billion billion units |
| quetta | Q | 1030 | One billion billion billion billion units |
| ronto | r | 10−27 | One unit divided by 1027 |
| quecto | q | 10−30 | One unit divided by 1030 |
The verbal equivalents make the scale easier to picture; the powers of ten are the formal definitions. For example, one ronnametre is 1027 metres, while one quectosecond is 10−30 seconds.
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How do the names and symbols compare?
The prefixes form two scale pairs: ronna and ronto use the exponent 27, while quetta and quecto use 30. The sign of the exponent determines whether the prefix multiplies or divides the unit. Symbol capitalization also matters: R and Q are large multiples; lowercase r and q are tiny fractions.
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- ronna (R): 1027, the large counterpart to ronto.
- ronto (r): 10−27, the small counterpart to ronna.
- quetta (Q): 1030, the large counterpart to quecto.
- quecto (q): 10−30, the small counterpart to quetta.
When were they adopted, and why?
The CGPM adopted the four prefixes on 18 November 2022 at its 27th meeting. The BIPM announced the decision on 19 December 2022. The official decision is recorded in Resolution 3 of the 27th CGPM, and the BIPM summarized the change in its announcement of the new SI prefixes.
The resolution said the additions would help scientific communities working with quantities outside the existing prefix range. It specifically pointed to data science’s anticipated need to express digital-information quantities above 1024. It also cited the importance of acting in time to prevent unofficial prefix names from becoming de facto conventions. That rationale does not mean every large data quantity requires a new prefix; the prefixes provide standardized options when such scales are useful.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Where do the new prefixes fit in the SI system?
They extend the official prefix range at both ends: quetta reaches 1030 for large multiples, and quecto reaches 10−30 for small fractions. The BIPM’s SI Brochure, 9th edition, version 4.01, records the 2022 decision in the official reference for the International System of Units.
These prefixes modify units; they do not create new units or change the meaning of the base unit. As with other SI prefixes, the prefix and unit symbol are written together, such as Qm for quettametres or qs for quectoseconds. Use the exact case specified for each symbol.
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