Ronnameters and quettagrams have joined the ranks of SI units

New prefixes in the International System of Units have been confirmed, ushering in ronto and quecto for small numbers and ronna and quetta for very large numbers, such as the amount of data on Internet servers

By Alex Wilkins

New prefixes for the world’s largest and smallest numbers were confirmed by a vote at the General Conference on Weights and Measures (CGPM) in Versailles, France, on Friday. Suggested prefixes are ronna and quetta for very large numbers and ronto and quecto for very small ones.

The International System of Units (SI) is a standard, accepted by most scientists, that underlies every measurement. In addition to defining things like the kilogram and the meter, it defines how very large and small numbers should be named.

The last extension of this naming scheme dates back to 1991, when numbers with 21 or 24 zeros were given the prefixes zetta (10²¹) and yotta (10²⁴) for the very large and the zepto (10^-21) and yocto (10^-24) for toddlers. There was little reason to use them back then, but the growing amount of data generated by the internet makes them more useful now – the amount of information is expected to reach 175 zettabytes by 2025.

“There’s already been quite a bit of speculation in the popular media about what could exceed a yottabyte,” says Richard Brown of the National Physical Laboratory, the UK’s measurement standards centre.

For example, brontobyte has been used informally by some to describe 10²⁷ bytes, while Google’s unit converter has long changed from 10²⁷ bytes in a hellabyte. But these don’t fit the SI naming scheme because the letters “b” and “h” are already used for prefixes or are commonly used for other units, Brown says, so adopting a standard now will ensure that alternative prefixes don’t get too deeply entrenched in the scientific literature.

Brown helped draft the proposal that GFCM member states voted on on Friday. Since there was no objection, the two new prefixes for numbers with 27 and 30 zeros became ronna and quetta for large numbers, and ronto and quecto for small numbers, respectively.

Although they will become SI prefixes with immediate effect, it may take some time for scientists to adopt them in their work.

Some scientists are skeptical of their usefulness. “We tend to define our own units, which are just useful in terms of the things we’re actually looking at,” says astronomer Mike Merrifield from the University of Nottingham, UK.

Brown suggests that ronto and quecto could have uses in radio astronomy, for example to measure the very low intensity of the cosmic microwave background, the radiation left behind by the big bang, but astronomers already frequently use the non-SI jansky for this , Merrifield said.

However, the benefits for science communication are clear, says Brown. “You’re going to be able to communicate what you want to say better if you use these standardized approaches.”

Although the names may seem random, they follow strict guidelines, Brown says. “R” and “q” were the only remaining letters in the English alphabet that had not been used by other prefixes, the middle of the words were loosely translated from the Greek or Latin term for how many times you must multiply 1000 par to get to the digits, he said, and the endings were due to the fact that large prefixes always end in “a”, while small prefixes end in “o”.

As for when we might see even bigger or smaller prefixes, Brown thinks we’ll be waiting at least 25 years. “It’s very difficult to predict the future, but I suspect it will definitely see me, I imagine, for my retirement and longer.”