Should We Spell Out Numbers Online?

] We face many difficult questions every day: Why do cats go crazy right before bedtime? Do aliens exist? Who will triumph on Game of Thrones? (No spoilers, please!) And of course, should we use digits or spell out numbers online?

Although I’ve yet to see an alien—and I only pretend to understand my cats—I was confident in my grasp of numbers until I read Hoa Loranger’s blog post “Break Grammar Rules on Websites for Clarity.” Hoa Loranger is a director at the Nielson Norman Group, a usability consultancy started by usability expert Jakob Nielson.

Loranger suggests using digits for numbers that “need to stand out” on websites because digits are easier to scan when searching for specific information. While I agree that digits can be easier to scan, this advice goes against the common belief that we should maintain consistency across print and web copy by following our style manuals and in-house style guides.

What do the style guides say about digits versus spelled out numbers?

The Chicago Manual of Style (Chicago) recommends spelling out general¹ numbers below 100,² while The Publication Manual of the American Psychological Association (APA) and The Associated Press Stylebook (AP) recommend spelling out general numbers below ten.³ The MLA Handbook, published by the Modern Language Association, recommends spelling out general numbers that can be written in less than three words (e.g., seven, twenty-one) and using digits for those requiring three or more words (e.g., 201, 51/2).⁴ In-house style guides typically establish standards for unique numeric situations that aren’t covered in Chicago, APA, AP, or MLA.

So, when should we use digits or spell out numbers in our online content?

Should we stick with our trusty manuals and guides? Or, should we use digits for any numbers that may be scanned by web visitors, while spelling out numbers deemed less important?

If your content is particularly number-heavy, you may want to follow Loranger’s advice to use digits for important numbers. However, I will continue to follow style manuals and in-house guides for the majority of content because number formatting will fall into chaos if we can’t agree on what “needs to stand out.” Plus, the entire purpose of style manuals and in-house guides is to avoid confusion by promoting uniform standards—standards that ultimately support usability.

Now about that last episode of Game of Thrones…

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1. All of the primary style manuals have detailed guidelines for using digits or words for very large numbers and specific numbers such as percentages, units of measurement, and currency. The use of words or digits can even change according to where numbers appear in sentences, so please consult your style manual or in-house guide.

2. The Chicago Manual of Style, 16th ed. (Chicago: University of Chicago Press, 2010), 9.2.

3. The Publication Manual of the American Psychological Association, 6th ed. (Washington, DC: American Psychological Association, 2010), 111–112; The Associated Press Stylebook 2016 (New York: The Associated Press, 2016), 198.

4. MLA Handbook, 8th ed. (New York: Modern Language Association of America, 2016), 92.