By Mary Morel
The International Standard ISO 1000:1992/Amd 1:1998 says millions should be abbreviated to ‘M’.
However, according to the Australian Style manual: For Authors, Editors and Printers (2002), ‘m’ is preferable to ‘M’ as long as the context is clear. It says: ‘The use of ‘M’ to represent ‘million’ is uncommon in Australia and is not recommended.’
This abbreviation should only be used in context of the dollar or other monetary symbol. Place the ‘m’ (unspaced and without a full stop) after the number.
Most writers spell out billion in text ($4 billion). The international abbreviation for billion is ‘G’, but in practice, I think most writers use ‘bn’ ($4bn).
Billions are tricky as there are different definitions for a billion. The Australian government style manual says:
‘The terms billion, trillion and quadrillion were originally used (as their prefixes suggest) to signify a million multiplied by a factor of two, three and four respectively.
billion = million x million (10 to the power of 12)
trillion = million x million x million (10 to the power of 18)
quadrillion = million x million x million (10 to the power of 24)
‘This convention has been overtaken internationally by the alternative approach that was instigated by French mathematicians and then adopted by the United States, whereby:
billion = thousand x million (or 1000 million, or 10 to the power of 9)
trillion = million x million (10 to the power of 12)
quadrillion = thousand x million x million (10 to the power of 15)
‘Australian and international standards (AS ISO 1000:1998) now acknowledge this as standard usage, affirming what has long been established in financial writing. However, scientists and statisticians usually avoid billion, trillion and quadrillion, preferring to express critical amounts using powers of ten.’
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