You Know the Kilo. Now Say Hello to the Quetta!

By: Alia Hoyt
Staff members inspect computer hardware at Gannan Data Lake
Staff members inspect computer hardware at Gannan Data Lake with a total storage capacity of 150PB (petabytes) March 17, 2022, in Ganzhou, Jiangxi Province of China. The ever-increasing data generated by servers prompted an increase in prefixes for large measurements. Zhu Haipeng/VCG via Getty Images

It's about to get easier for people to communicate about really big and really tiny numbers. The prefixes ronto, quecto, ronna and quetta are joining the likes of kilo, tera, mega and many other existing terms in the metric system of measurement. These new prefixes are the first expansions since 1991.

The shift in the International System of Units (SI) was finalized at a vote Nov. 18, 2022, at the General Conference on Weights and Measures. Scientists deemed it necessary because scientific advancements are rapidly approaching the limits of how we can refer to huge and small numbers. The internet is a major reason for this, as the growing amount of data on servers worldwide is set to exceed existing numbers in the next few years. This means that there needs to be a standard unit of measurement in place, so that scientific communication doesn't get all discombobulated.


At the same time, advancements in radio astronomy, such as measuring the radiation left over from the Big Bang 13.8 billion years ago, have revealed a need to label exceedingly tiny numbers. Current measurement standards simply can't go that small without adding a bunch of filler jargon, "like one thousand-thousandth of" a given unit. Hence the need for these new prefixes.

What Are Ronnas, Quettas, Rontos and Quectos?

The new prefixes for extra large numbers are ronna and quetta. Before these were approved, yotta was the largest prefix and equaled a number 1 followed by 24 zeros (that's 10 to the 24th power or 1024).

  • Ronna, by comparison, is a number 1 plus 27 zeros: 1,000,000,000,000,000,000,000,000,000 or 1027).
  • Quetta dwarfs ronna, however, as that prefix is equivalent to a whopping 30 zeros (10 30).

For contrast, the kilo is only 10 3. The giga is 109, the tera is 1012 and the peta is 1015.


Super-small numbers have two similar, yet unique prefixes.

  • Ronto is equivalent to 10 to the negative 27th power or 10-27.
  • Quecto is even tinier, at 10 to the negative 30th power (10-30).

Before they hit the scene, yocto was the smallest expression, at 10 to the negative 24th power or 10 -24. Other small measurements are the centi (10-3), the nano (10-9) and the pico (10-12).


Why Were These New Measurements Added?

Scientists already had a need to discuss such large and small numbers but lacked the official terminology to do it with. So, many of them made up their own terms, like "hella" and "bronto," but this can get pretty confusing. When those terms started to hit the mainstream media, the powers-that-be at SI decided to make some tweaks. They couldn't just use the terms that were already in casual use, however, as metric prefixes are always shortened to be only the first letter (K for kilo, for example). Measurement terms starting with H and B were already spoken for, so that's why hella and bronto couldn't be considered candidates.

"The only letters that were not used for other units or other symbols were R and Q," said Richard Brown, head of metrology at the U.K.'s National Physical Laboratory, according to a ScienceAlert article. Brown helped to draft the proposal for the new numbers. "The middle of the words are very, very loosely based on the Greek and Latin for 9 and 10." Also part of the naming conventions: Smaller measurement prefixes always end in O, and larger ones finish off with an A.


Brown added that additional larger and smaller numbers should not be necessary for 20 to 25 more years, when it's likely that science will continue to break barriers, once again.