Question: Which of these abbreviations are correct?
$25 m $25m $25M $25mm $25mil
Answer: None of them if the reader does not understand them.
Last week I heard from David, a proofreader in international banking, who wrote about standard abbreviations for millions and billions. In an industry in which a typographical error can have big consequences, he has a reason to be concerned.
My research led me to the answer above. No abbreviations are correct unless the reader recognizes them and agrees with the writer about what they mean. Here is the rule in short:
When there is room for doubt, spell it out.
Checking my usual main resources–Microsoft Manual of Style for Technical Publications, The Associated Press Stylebook, The Chicago Manual of Style, and The Gregg Reference Manual—I found that none of them recommends any abbreviations for thousand, million, or billion. Apparently, there is simply too little agreement on their meaning. The Gregg Reference Manual points out this problem, for example:
In Roman style, 48M means 48,000; in metric style, 48M means 48,000,000.
I wish my bank would interpret my $48,000 as $48,000,000, but I don’t think it is going to happen. Therefore, I will continue to teach business writing. Take one of our courses here!