In British English, a billion traditionally had a different meaning to in American English (10^12). In modern writing the American convention has pretty much taken over. Is it therefore okay in a British publication to write 'billion' and assume the meaning will be unambiguous (e.g. 'approximately one billion years old'), or should the figure (or SI equivalent e.g. G, Ga) always be stated still to ensure clarity?

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    I don't think million ever meant 10^9, it's been always 10^6. The differences were over billion, and whether billion meant a million millions, i.e. 10^12, or a thousand million, 10^9.
    – Bryan Krause
    Jul 19, 2017 at 18:30
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    When in doubt, aim for unambiguous language -- that's what the SI equivalents are there for, after all.
    – tonysdg
    Jul 19, 2017 at 19:43

2 Answers 2


It would be unusual to me to see million or billion used in academic scientific contexts, except for a few cases where there would be absolutely no ambiguity (number of people on earth or age of rocks, for example, would only fall under the American/modern usage of billion), and even in those contexts, only for loose descriptions (versus reporting of data). (I did a brief Google Scholar search for both million and billion; although there were many many results, most seemed to be referencing either authors surnamed Million or Billion, or the use of the terms in these loose forms or in the context of geology, as in "three billion year-old rocks)

I can't think of a circumstance where scientific notation or use of SI prefixes would be a problem when writing for an scientific academic audience. If writing for a lay audience or outside the hard sciences, it might make more sense to use million/billion: most respectable outlets will either have a style guide or refer to another established style guide for proper procedure. It seems like the BBC and University of Cambridge embrace the 10^9 billion and do not caution specifically against its use, only noting the previous definition. Certainly in no context should you use billion to mean 10^12.

  • Thanks. I'm reproducing a figure that uses it so it got me curious about this in a more general context. I'll edit the figure. Jul 19, 2017 at 20:58
  • Your first sentence implies that there is sometimes ambiguity about whether billion means 10^9 or 10^12. There is no ambiguity! You should trust someone who knows, not try to guess by looking on the web. (I suppose my comments are merely "on the web" too, but you know what I mean.) Other points: Are you saying that the BBC and Cambridge webpages don't caution specifically against the use of the word "billion"? Of course they don't - it is a common word. And your view that "million" and "billion" should not normally be used in academic writing might be reasonable, but it is a separate issue.
    – user72102
    Jul 20, 2017 at 7:45
  • So if I should not use "billion", how would I say The bacteria population grew to x. if x=3*10^12? 3 Terabacteria? Jul 20, 2017 at 9:30
  • I agree with problemofficer. A country's population or a number of genetic variants might also be something like 3.27 million. So I don't think that Bryan Krause's view about that is reasonable, on second thoughts.
    – user72102
    Jul 20, 2017 at 10:44
  • @problemofficer If you are talking about a bacterial population, you are probably talking about a volume, and often using Colony Forming Units for the actual count. "The bacterial population grew to 3*10^12 CFUs/L."
    – Bryan Krause
    Jul 20, 2017 at 15:14

The American meaning has completely taken over in the UK, and this has been true for at least 25 years. If you don't believe me then look at British newspapers from 1990. So it is most definitely OK in a British publication to assume that billion means 10^9.

From a 2011 BBC News article article:

In 1974, Harold Wilson pledged that the British government would adopt the "short scale" naming system used in the US to avoid ambiguity. As a result, the value of billion is now generally understood to mean a thousand millions. Nonetheless this is still a bone of contention for many, and the older sense "a million millions" is still common.

The last sentence is wrong. The older sense has not been common for several decades, though I suppose it might be used privately by eccentric people.


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