# New SI prefixes and their etymology

Five months ago I wrote a post speculating about new SI prefixes. I said in this post “There’s no need for more prefixes; this post is just for fun.”

Well, truth is stranger than fiction. There are four new SI prefixes. These were recently approved at the 27th General Conference on Weights and Measures. Here is the resolution (in French).

The new prefixes are:

• 1030 quetta (Q)
• 1027 ronna (R)
• 10−27 ronto (r)
• 10−30 quecto (q)

The names were the suggestion of Richard J. C. Brown. He gives seven desirable properties of new names:

1. The names should be simple and, if possible, meaningful and memorable.
2. The names should have some connection to the powers of 103 that they represent.
3. The names should be based on either Latin or Greek as the most used languages previously.
4. Multiples should end ‘-a’ and sub-multiples should end ‘-o’.
5. The symbols used should be the same letter for a given power of ten, in upper case for multiples and in lower case for sub-multiples.
6. Letters already in use for SI prefixes, SI units, other common units, or symbols that may otherwise cause confusion, should be avoided.
7. Following the precedent set recently, letters should be used in reverse English alphabetical order, suitably modifying chosen names, and skipping letters as appropriate.

OK, so how does that lead to the new prefixes? Point #4 explains the last letter of each prefix.

Brown says that the etymology of ronna and ronto is

Greek & Latin, derived from ‘ennea’ and ‘novem’, suggesting 9 (ninth power of 103)

and that the etymology of quetta and quecto is

Latin, derived from ‘decem’, suggesting 10 (tenth power of 103).

That’s quite a stretch.

The largest prefix had been zetta and yotta, so Brown wanted letters that came before Y in the alphabet. P was already used (peta and pico) and the next two unused letters were Q and R. So the prefixes for 1030 and 1027 begin with Q and R.

Presumably ronna uses an O because yotta had an O for the second letter. And the next letter N comes from the N’s in ennea and novem.

It seems quetta used the Q sound because Q was the next letter available, and an allusion to the hard C in decem. The “etta” part is reminiscent of zetta.

## 3 thoughts on “New SI prefixes and their etymology”

1. Appreciated.
Copied to my year 9 kid and the math teacher. We are in the land of Oz, downunder.

2. Reminded of Fermi’s quote, “If I could remember the names of all these particles, I would have been a botanist.”

3. TheTribeofDAN

#MyChart go to 13 , so i’m still looking for 33 , 36 , & 39 +\- .
i’m thinking #Biblical …
39-geno/gena ,
36-levo/leva ,
33-duto/duta .
& what’s with exa/atto ?
it don’ match .
Sincerely, DANIEL