Virtually everything that environmental, health, and safety (EHS) professionals write contains numbers, but how many people know the proper way to style (write-out) numbers in text? Mark Nichols’ article, How to Style Numbers, which appeared on the website Daily Writing Tips, provides an excellent refresher.

According to Nichols, the two most important style guides are the Chicago Manual of Style, which is the bible of the book publishing industry, and the AP Stylebook, the authority of record for newspapers. Although magazines generally select one style or the other, websites tend to use AP style. The more formal the writing, the more likely an author is to follow Chicago style.

The basic Chicago rule is to spell out numbers from one to one hundred but use numerals for 101 and up. But if you refer to two amounts in the same category, default to numerals. (“I found 137 mistakes, compared with only 89 last time.”) Major exceptions to the basic rule include a number as the first word in a sentence, larger round numbers (“five hundred”) and orders of magnitude (“millions,” “billions,” etc.). The point is to maintain consistency as much as possible.

Technical, statistically dense text, meanwhile, is better served by numerals, so in that case use digits for physical dimensions, degrees (both of temperature and angle), scores and percentages, money, time, and other references to quantity.

Less formal writing, including most online content, tends to follow the AP style:

Spell out numbers only to ten, use numbers for 11 and up, and don’t be concerned about matching style when you refer to quantities on both sides of the tipping point. (“In a classroom poll conducted recently, only seven of 29 students agreed with that statement.”)

Numbers and Hyphens

Nichols notes that a hyphen is not needed for physical dimensions, but should be used when a number modifies a noun (e.g., “a tank containing 25 gallons of gas,” versus “a 25-gallon gas tank”). Futhermore:

Hyphenate double-digit numbers by themselves — and within larger numbers — if they aren’t multiples of ten (“sixty-four,” “one hundred twenty-eight”), but don’t hyphenate all the elements of a large number like a chain.

Simple and mixed fractions should be styled, depending on your preferred policy, either like “1/2” and “1 3/4,” or like “one-half” or “one and three-fourths.”

More Information

Refer to Daily Writing Tips for more information on writing style and how to improve your writing.

Photograph: Morning Paper by Crissy Pauley.

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