AP Style vs. Chicago Style

As a writer, it can sometimes be difficult to transition between writing styles and formats like Chicago style and AP style. For example, I could be asked to write a press release, and then move on to a software documentation project. Although most of the grammar and mechanics are the same, certain styles have particular punctuation and other small, yet significant, variations. It’s easier to remember these differences when you consider the industries in which they are used. AP style writing supports quick, space-restricted content (e.g., newspapers, online articles). Chicago style writing fancies lengthier, more detailed materials (e.g., books, technical documentation).

When I find myself having to transition from one style to another, such as AP to Chicago, it helps to remember some of the most glaring differences between the two.

1. Abbreviations

Abbreviations are always a tricky subject, especially when referencing states.

  • Per AP style, most state names are abbreviated following the name of a city. The exceptions are Alaska, Hawaii, Idaho, Iowa, Maine, Ohio, Texas, and Utah. The AP style guide also specifies a list of 30 U.S. cities that do not require state identification.

    • My mom has lived in Norfolk, Va., Seattle and Akron, Ohio.
  • Per Chicago style, state names are spelled out following city names. When abbreviations are used, Chicago uses the two-letter postal code abbreviations.
    • On our road trip, we drove from Memphis, Tennessee, to Jacksonville, Florida.

Remember, AP tends to be more abbreviated.

2. Dashes

Though the em dash typically has the same usage, one tricky issue is the spacing that accompanies them.

  • AP style em dashes (—) have a space before and after.
    • Andy was happy to hear the good news — he had waited all week.
  • Chicago style em dashes do not have spaces before or after.
    • Kathleen and Paul are celebrating their wedding anniversary40 years together.

3. Ellipses

Another commonly (mis)used or inconsistently used punctuation is the ellipsis.

  • Per AP style, the ellipsis has a space before and after the three period marks.
    • Chocolate is … bliss.
  • Per Chicago style, the ellipsis consists of three periods with spaces before and after each one.
    • I love . . . naps.

Again, if you keep in mind that AP style embraces brevity, this will be easy to remember.

I remember this rule because AP reminds me of “Add Space.” Also, although the spaced em dash is very long, do not substitute an en dash in its place. Em dashes, en dashes, and hyphens are not the same. In both AP and Chicago styles, the en dash is used to depict a range (e.g., I ate between 4–7 strawberries, and Jill said the best time to pick them is July–September.)

4. Numbers

Editing articles with numbers can sometimes cause me to second guess whether I’m using numerals and written-out numbers properly.

AP style tends to use numerals rather than spelling out whole numbers. However, particular categories, such as percentages, have separate rules.

Chicago style prefers to spell out numbers that are less than 100. However, Chicago style has additional guidelines for numbers, such as for percentages, where this general rule does not apply. Also, “like” categories are treated the same. For example, if “100 cats” are referenced in the copy, then “4 cats” is correct.

AP Style Chicago Style
In general

Spell out numbers less than 10.

However, use numerals before measurements and for ages, events, or things; for all tabular items; and for percent and percentages.

In non-technical copy, spell out numbers less than 100. (Alternate rule: spell out numbers less than 10.)

However, use numerals with certain categories, such as percentages. And the use of numerals in some cases is guided by common sense.

  • 5-year-old cat
  • the cat is 5 years old
  • 10-year-old daughter
  • seven-year-old dog
  • sixty-year-old man
  • 100-year-old building
Measurements 5-foot wall

General rule: sixteen kilometers

Common sense: 5 feet, 8 volts, size 4 skirt

  • 8 cents
  • 15 cents
  • $3.67
  • a dollar
  • $500,000
  • $300 million
  • ninety-five cents (but 95₵)
  • eighty-six dollars (but $86.00)
  • 7 percent
  • 15 percent
  • 6 percentage points

Humanistic copy: 8 percent, 100 percent

Scientific copy: 20%

  • temperatures rose 4 degrees
  • the temperature is 96 degrees Fahrenheit
  • the temperature rose to zero
  • it was 7 degrees below zero

Non-technical copy: temperatures rose thirty degrees, the temperature reached 100 degrees

Scientific copy: 60°F

5. Serial (Oxford) Commas

The serial or Oxford comma is often argued regarding its proper usage (if any) by editors, writers, and even readers. It’s important to get it right. Incorrect comma use is already one of the most common writing errors even without introducing style variations. To me, the serial comma is one of the most significant differences between AP style and Chicago style.

  • Per AP style, the serial comma is to be avoided.
    • Jacob enjoys novels by Bradbury, Tolkien and Salinger.
  • Per Chicago style, the serial comma is highly recommended.
    • Katlyn’s favorite authors are Twain, Hemingway, and Steinbeck.

A helpful tip to remember this rule is “Chicago” and “comma” both begin with the same letter; therefore, in Chicago style, always use the serial comma.

These are just a few standard situations that I often come across as an editor. If you are like me, it can sometimes be frustrating when switching from one project to another. It’s good to develop your own habits and ways of remembering some of the major differences between AP and Chicago styles, or feel free to borrow mine. It can help keep your writing and editing consistent, clear, and correct. Or, if you prefer, consistent, clear and correct.

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