Proofreading Tips: Numbers in AP Style

Created by journalists to help standardize public-facing writing in 1953, The AP Stylebook is still one of the most commonly used American English style guides around. As a proofreader, you’ll often need to check the formatting of numbers when working with a client who writes in AP style. This post will take you through how to write different kinds of numbers in AP style.

Basic Rules for Numbers in AP Style

The general principles recommended in The AP Stylebook for writing numbers are to:

  • Writers should present numbers up to nine as words.
  • Writers should present the numbers 10 and above as numerals.

These rules apply to both cardinal and ordinal numbers. However, AP style also has plenty of specific guidelines for using numbers in different situations, which we will outline below.

When to Use Numerals in AP Style

When reviewing your client’s work, make sure they use numerals for:

  • Measurements (e.g., 30 seconds, 90 yards, 60mph).
  • Monetary units (e.g., £5, $6 bill).
  • Mathematical equations (e.g., 2 + 2 = 4), decimals (e.g., 8.4), percentages (e.g., 6.3%), and fractions with numbers larger than one (e.g., 2 ¼). The key exception here is simple fractions under one (e.g., authors should write the likes of two-fifths and three-quarters as words).
  • Odds, proportions, and ratios (e.g., 9-1 chance, 3 parts egg to 4 parts flour).
  • Times, dates, years, and decades (e.g., 7 pm, Feb. 20, 1968, the 90s).
  • Numbers in highways and political districts (e.g., Highway 1, 9th Precinct).
  • Vehicle names (e.g., Apollo 9).
  • Court decisions and votes (e.g., the court ruled 5-4, 3-vote margin).
  • Military ranks used as titles before names (e.g., 1st Sgt. Dean Rodgers), other military terms (e.g., 6th Fleet), and weapons (e.g., 9mm pistol). However, ranks should be spelled out when used after or without a name (e.g., John is a second lieutenant).
  • Ranks and rankings (e.g., He was our no.1 choice, Top 40).
  • Numbers relating to sequences, unless they are used descriptively (e.g., page 1, size 4, Act 3, but The plot twist happened in the third act).
  • Numbers in tables and statistics.
  • Sports scores (e.g., 1-0, 5 under par)

Keep an eye out for these types of numbers in your client’s work.

When to Spell Out Numbers in AP Style

There are a few cases where your client should always spell out a number in full. These are:

  • At the start of a sentence, except for years (e.g., Twenty people saw the meteor, but 2020 saw the rise of knitting). If you spot a number at the start of a sentence, you can either spell it out or see rearrange the sentence so the numeral comes later on.
  • In indefinite and casual uses (e.g., two at a time please, she ran half a kilometer).
  • In proper names (e.g., The Fantastic Four, Famous Five), figures of speech (e.g., nine to five, a picture is worth a thousand words), and traditional usages (e.g., The Ten Commandments).
  • In fractions less than one (e.g., they increased their revenue by three-quarters last year).

These cases usually overrule the conventions of numerical use, so it’s especially important that you double-check your client’s use of numerals against them!

Large Numbers in AP Style

AP style advises writing large round numbers as a mixture of letters and numbers:

Some have predicted that the human population will peak at 9 billion.

Experts estimated the cost of repairs to the city at $150 million.

However, this only applies to round numbers (i.e., thousands, millions, or billions). Other, more complex large numbers should be written as numerals (e.g., 1,840,253, not one million eight-hundred-and-forty thousand two hundred and fifty-three).

Roman Numerals

Your client’s use of Roman numerals should fall under one of the following categories:

  • Wars (World War I, World War II)
  • The titles of monarchs (King Henry VIII)
  • Certain legislative acts (Title IX)

As a general rule, AP style advises using Roman numerals sparingly. So you’ll need to make the correction for your client if you see any besides the examples above.

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