When (and how) to spell out numbers as words: Explanation and examples

General rules for writing numbers

It can be confusing to figure out when to type out numbers and when to use numerals. A common misconception is that all style guides follow the rule to spell out numbers nine and below and use numerals for 10 and above. While this is common, there aren’t any universal rules for writing numbers unless you’re writing for a specific style guide.

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How to spell numbers: Rules by style guide

Choosing a style guide to follow depends on the purpose of and audience for your writing. Here are the most common style guides you’ll encounter in academic and professional writing—do note that highly specialized fields or government work often come with their own strict style guidelines.

AP Stylebook

AP Style, also known as Associated Press Style, is typically used in reportage or in other news-related contexts.

For AP:

• Spell out numbers nine and below; use numerals for numbers above 10.
• Avoid starting sentences with numbers; most can be spelled out, but years must appear as numerals, so try to write the sentence a different way.
• Unless there are minutes to add to the hour, time of day is just one number.
• Money is always expressed in numerals.

APA Manual

The American Psychological Association (APA) Style Manual isn’t the niche publication it’s title may imply. This infrequently updated style manual is often used in research writing and scientific writing.

For APA:

• Numbers nine and below are spelled out; 10 and above appear as numerals.
• Spell out numbers that start sentences even if they’re above 10.
• Spell out numbers that appear in common phrases no matter how large they are.
• Numerals should always be used for measurements, fractions, ratios, percentages, money, ages, dates, and times.
• Numbers in a series should always appear as numerals; any adjective before the numeral should be capitalized, e.g., Level 3 or Edition 17.

Chicago Manual of Style

The publishing industry— books and non-news magazines—typically follows the Chicago Manual of Style (CMoS). Humanities writing often follows the rules of CMoS, too.

For CMoS:

• Spell out numbers zero through one hundred; all whole numbers should be spelled out, e.g., twelve thousand.
• Spell out numbers at the beginning of a sentence.
• Spell out large, whole, round numbers—unless they’re amounts of currency, then use numerals.
• Fractions should be written with numerals unless they begin a sentence.

MLA Handbook

Modern Language Association (MLA) format is ubiquitous in high school and college academic settings. If you’re writing academically and aren’t being required to adhere to another style guide, this is typically what you should follow in your work.

For MLA:

• Spell out any number that would only take one or two words to write.
• Those two-word numbers? Hyphenate them, e.g., ninety-nine.
• Spell out numbers at the beginning of a sentence.

However you choose to handle writing out numbers in your work, stay consistent throughout. There should be an internal logic to your choices to help ensure clarity.