Here’s a great question I got recently from a reader named David: “When it comes to numbers, I have always heard one through nine are to be spelled out and then 10 and on are to be numerals. Does a person celebrate their 6th birthday or their sixth birthday? Are they then six-years-old or 6-years-old? Also, how do you handle things like 6.32%?
"Should it be six-point-three-two-percent? Also, is it November seventh or November 7? Why do most newspapers and magazines use November 7 and not November 7th? … I'm SO confused.”
The good news, I told David, is that there’s no right or wrong way to write numbers. There is only style.
In editing, style means the rules laid out in the Associated Press Stylebook, the Chicago Manual of Style or any other guide created for consistency within a publication. The key word is consistency.
Though both “an eight-year-old” and “an 8-year-old” are legitimate choices, you don’t want both to appear in the same article, book or document. So the style guides serve as playbooks to prevent unsightly inconsistencies.
These guides’ rules for writing numbers apply only to professional editors. The rest of us don’t need to worry about them. You can write November 7 or November 7th as you like. But any time you want your writing to look professional, you can follow some of their cues.
The style guides’ rules for writing numbers are too numerous to memorize. For example, news style says to use numerals for figures greater than nine unless that number begins a sentence, but makes an exception to that exception when the number happens to be a year. So you’d write: “I have 1,976 marbles” but “One thousand nine hundred seventy-six is the number of marbles I have” but “1976 was a great year for democracy.” And there are more rules for ages, fractions, ordinal numbers, decimals, percentages, measurements and on and on.
Book style leans more toward spelling things out, so in this style you spell out not just numbers less than nine but above, too. But Chicago style also has tons of exceptions, especially for numbers that would be too cumbersome to spell out.
So if you want to do it exactly like the pros, you must consult a style guide. But if you just want a simple system for writing numbers in a clean, professional way, consider adopting the following suggestions, which I gleaned from news style basics.
In general, spell out numbers nine and below, using numerals for numbers 10 and above. Use a combination of numerals and words for very big round numbers like 4 million and 23 billion, but use numerals for oddballs like 4,122,878.
Make all measurements, percentages, decimals and ages numeric. For ages, hyphenate a compound used as a noun, “He is a 9-year-old,” and as an adjective in front of a noun, “They have a 9-year-old child,” but otherwise no hyphens: “He is 9 years old.” (Note, however, that a 6-year-old celebrates his sixth birthday because, in this context, “sixth” is not an age but a point in a sequence. So it’s not an exception to the rule of spelling out numbers less than 10.)
Don’t begin a sentence with a numeral unless it’s a year — either spell out the number or find a way to move it to another place in the sentence.
And feel free to spell out casual uses whenever doing so seems more logical to you: “If I told him once I’ve told him a million times.”
Or you can disregard everything I said and make up your own style. As long as you’re consistent, you can’t go wrong.
JUNE CASAGRANDE is author of “It Was the Best of Sentences, It Was the Worst of Sentences.” She can be reached at JuneTCN@aol.com.