The metric system gains new prefixes. Here’s what you need to know

Discover the new prefixes of the metric system: ronna-, quetta-, ronto- and quecto-.

Adopted on November 18 at the 27th General Conference on Weights and Measures in Versailles, France, ronna- and quetta- describe excessively large numbers while ronto- and quecto- describe the extremely small. This is the first time that the International System of Units, or SI, expanded since 1991, when the prefixes zetta-, yotta-, zepto and yocto- have been added (SN: 01/16/93).

Numerically, ronna- is 10²⁷ (it is a number followed by 27 zeros) and quetta- is 10³⁰ (30 zeros). Their lowercase counterparts ronto- and quecto- also refer to 27 and 30 zeros, but these come after a decimal point. Until now, yotta- and yocto- (24 zeros) capped the range of the metric system.

Science News spoke to Richard Brown, head of metrology at the National Physical Laboratory in Teddington, England, about what the latest extension of the SI means for science. The following conversation has been edited for clarity and brevity.

NS: Why do we need the new prefixes?

Brown: The amount of data in the world is growing exponentially. And we expect that to continue to increase and probably accelerate due to quantum computing and digitalization and things like that. At the same time, this amount of data is starting to approach the high end of the prefixes we currently use. People are starting to wonder what comes next?

NS: Where do prefix names come from?

Brown: About five years ago I heard a BBC podcast about these new names for oodles of data. And the two they mentioned were brontobyte and hellabyte. Brontobyte I think comes from brontosaurus being a big dinosaur and hellabyte comes from “hell of many”.

The problem with those from a metrology point of view, or from a measurement point of view, is that they start with the letters B and H, which are already used for other units and prefixes. So we can’t use them as names. [It was clear] that we had to do something official because people were starting to need these prefixes. R and Q aren’t used for anything else, really, in terms of SI units or prefixes. [The prefix names themselves are] very, very loosely based on the Greek and Latin names for nine and 10.

NS: How will the prefixes be used?

Brown: The whole point of the International System of Units is that it is an accepted worldwide system, which if you use it, you will be understood.

When you use a prefix with a unit, it means that the number associated with the unit changes. And people like small numbers that they can understand. So you can express the mass of the Earth in terms of ronnagrams; it’s six ronnagrammes. And also the mass of Jupiter is two quettagrams. Some good examples of [small numbers] are that the mass of an electron is about a rontogram, and the mass of a bit of data stored on a mobile phone is about a quectogram.

I think using an appropriate prefix makes things more understandable. And I think we have to remember that even if there is not always a direct scientific use in the immediate future, they will gain ground over time.