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Expansion to the SI prefix range

Introducing the new SI prefixes: ronna, quetta, ronto and quecto

NPL leads expansion to the SI prefix range for the global metrology community

In November 2022, measurement scientists and government representatives from around the world voted at the General Conference on Weights and Measures (CGPM) to expand the range of prefixes used within the International System of Units (SI).

This decision means that four new prefixes (two at the top end of the SI range and two at the bottom end of the SI range) can now be used to express measurements worldwide. This is the first expansion to the SI prefix range since 1991.  

Watch our animation to find out more >>

What are the new SI prefixes and why do we need them? 

The proposal, led by Prof Richard Brown, Head of Metrology at NPL, recommended the four new names. 

The new names for very large numbers are: 

  • ronna (symbol R) for 1027 or 1 000 000 000 000 000 000 000 000 000  

  • quetta (symbol Q) for 1030 or 1 000 000 000 000 000 000 000 000 000 000 

They are joined by their tiny counterparts: 

  • ronto (symbol r) for 10−27 or 0.000 000 000 000 000 000 000 000 001 

  • quecto (symbol q) for 10−30 or 0.000 000 000 000 000 000 000 000 000 001 

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 (yottabytes and zettabytes, for expressing huge quantities of digital information). The prefixes for very small numbers are useful for quantum science and particle physics. However, these can be used with any SI unit, for example in the future we can be expected to talk about ronnametres and quettagrams.

The SI prefixes explained

The SI prefixes are an essential part of the International System of Units, allowing us to extend the use of the SI as widely as possible, and ensuring the effective and unified communication of measurements across technical disciplines, without the requirement to use or create non-SI units.

When our measurements get very large (or very small) the numbers we use to express these measurements using SI base units or SI derived units also become very large (or very small) and so more difficult to interpret. For instance 0.0045 m or 34 000 000 000 W. 

The SI prefixes can be attached to the SI base units or SI derived units to form new multiples (or sub-multiples) of these units. When expressing the same measurement, changing the size of the unit has the effect of also changing the number used with the unit. If a suitable SI prefix is used this makes the measurement much easier to interpret and communicate. For instance 0.0045 m becomes 4.5 mm (millimetres), because 1 mm = 0.001 m, and 34 000 000 000 W becomes 34 GW (gigawatts), because 1 GW = 109 W.

Multiplying Factor Name (symbol) Scientific Notation
1 000 000 000 000 000 000 000 000 000 000 quetta (Q) 1030
1 000 000 000 000 000 000 000 000 000 ronna (R) 1027
1 000 000 000 000 000 000 000 000 yotta (Y) 1024
1 000 000 000 000 000 000 000 zetta (Z) 1021
1 000 000 000 000 000 000 exa (E) 1018
1 000 000 000 000 000 peta (P) 1015
1 000 000 000 000 tera (T) 1012
1 000 000 000 giga (G) 109
1 000 000 mega (M) 106
1 000 kilo (k) 103
100 hecto (h) 102
10 deca (da) 101
1   100
0.1 deci (d) 10-1
0.01 centi (c) 10-2
0.001 milli (m) 10-3
0.000 001 micro (µ) 10-6
0.000 000 001 nano (n) 10-9
0.000 000 000 001 pico (p) 10-12
0.000 000 000 000 001 femto (f) 10-15
0.000 000 000 000 000 001 atto (a) 10-18
0.000 000 000 000 000 000 001 zepto (z) 10-21
0.000 000 000 000 000 000 000 001 yocto (y) 10-24
0.000 000 000 000 000 000 000 000 001 ronto (r) 10-27
0.000 000 000 000 000 000 000 000 000 001 quecto (q) 10-30

Find out more about the SI units

Learn more about the SI base units and why they are imperative for everyday measurements.

SI units

SI mnemonic challenge

Our SI mnemonic is now closed, check back soon to discover the winners.

Mnemonic challenge
 

Meet the scientist behind the changes

Learn about Richard's background, experience and special interest areas.

Meet Prof Richard Brown

SI posters for schools

NPL supports science learning in schools. Check out our posters covering the SI base units and measurement.

Download school posters

Save the SI bots

Download our app and help the Keeper of Measurements in their quest to save the SI bots and restore the world of measurement before chaos hits!


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