One thing I noticed recently when looking through some reports is that thousands are often abbreviated, in a similar way to scientific measurements are abbreviated.

E.g. $1,000,000 becomes $1m and £20,000 becomes £20K

I was curious about the capitalisation choices though, and the fact that they appear to be the opposite of what SI would specify for kilo- (k) and mega- (M).

Does anyone know where these monetary abbreviations came from and why they're capitalised in this way?

  • These are power prefixes and they are capitalized as units of measurement.
    – Gigili
    May 9, 2011 at 11:56
  • This is also common in computing, where people use KB instead of kB. (At least that's clearer than when they confuse B and b, though.) May 9, 2011 at 13:57
  • @Matthew Read: At least most people who talk about Kb and KB agree that the K part means 1024, not 1000. Although sellers of computing hardware invariably interpret Giga, Mega, and Kilo according to the lower value, so they can quote higher specs than more honest competitors. May 9, 2011 at 16:06
  • @FumbleFingers Yep, that's a whole other issue. I personally use KiB for 1024 bytes. Related: xkcd.com/394 May 9, 2011 at 16:12
  • 1
    @FumbleFingers: Not invariably... Sometimes when describing storage media the units are based on 1000, sometimes 1024. Especially interresting was the 1.44 MB floppy, where M neither ment 1000*1000 nor 1024*1024, but 1000*1024...
    – Guffa
    May 9, 2011 at 18:24

3 Answers 3


When used for money, it seems like there are no rules at all for the capitalisation, at least no rules that are followed by a majority.

A quick search reveals that both M and m are used for millions, and both K and k are used for thousands.

The origin of the monetary units are most likely the same as for the SI units, but they have been adopted by the economic sphere and live their own lives.

  • 1
    I also guess that, when speaking of money, you'd be very unlikely to use m as in milli-, so there is no confusion between m and M in this case.
    – nico
    May 9, 2011 at 15:45

Because prefixes such as k and M are common, and not reserved to scientists who know and understand the SI recommendations. If you look at results from this Google search, you'll see it has both lowercase and uppercase M in roughly equivalent amounts.


Because they aren't standards for money. Economists use 'M' for thousands and 'MM' for millions

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.