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Abbreviating Big Numbers

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Lynn Gaertner-Johnston Updated on

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!

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By Lynn Gaertner-Johnston

Lynn Gaertner-Johnston has helped thousands of employees and managers improve their business writing skills and confidence through her company, Syntax Training. In her corporate training career of more than 20 years, she has worked with executives, engineers, scientists, sales staff, and many other professionals, helping them get their messages across with clarity and tact.

A gifted teacher, Lynn has led writing classes at more than 100 companies and organizations such as MasterCard, Microsoft, Boeing, Nintendo, REI, AARP, Ledcor, and Kaiser Permanente. Near her home in Seattle, Washington, she has taught managerial communications in the MBA programs of the University of Washington and UW Bothell. She has created a communications course, Business Writing That Builds Relationships, and provides the curriculum at no cost to college instructors.

A recognized expert in business writing etiquette, Lynn has been quoted in "The Wall Street Journal," "The Atlantic," "Vanity Fair," and other media.

Lynn sharpened her business writing skills at the University of Notre Dame, where she earned a master's degree in communication, and at Bradley University, with a bachelor's degree in English.