When to spell out numbers in your book: Chicago's rules, the exceptions, and examples
In a book that follows The Chicago Manual of Style, the standard for most US book publishing, the short answer is: spell out zero through one hundred, use numerals above that, and spell out any number that starts a sentence. Then keep numbers of the same kind consistent. Here are the rules, how they differ from news style, and examples.
Chicago's three main rules
Chicago's blog, CMOS Shop Talk, summarizes the rules most book editors follow:
- Spell out zero through one hundred in general text, and use numerals above that (CMOS 9.2).
- Spell out a number that begins a sentence (CMOS 9.5). If spelling it out is awkward, rewrite so the number comes later.
- Be consistent within a category. Chicago recommends the same styling for all the numbers in a sentence or paragraph that refer to the same kind of item (CMOS 9.7). The same post notes that readability can outweigh consistency, and that you can break a rule if it is not working well.
How AP style differs
News writing usually follows the Associated Press Stylebook, which spells out only one through nine and uses numerals from 10 up. The CMOS Shop Talk post also notes that AP spells out numbers at the start of a sentence but makes an exception for years and for expressions that mix numbers and letters, such as 401(k). If your book will be published by a book publisher, expect Chicago; if you write for a news outlet, expect AP.
Examples
| Chicago style | Why |
|---|---|
| She interviewed forty-two founders. | Zero through one hundred: spell out |
| The survey had 350 responses. | Above one hundred: numerals |
| Twelve chapters made the final cut. | Starts a sentence: spell out |
| The final cut kept 12 of the 140 chapters drafted. | Same kind of item in one sentence: numerals for both |
| We met on page 56 of the proof. | Page numbers are conventionally numerals |
Examples written by Scribe Media. Chicago has further rules for dates, money, percentages, times and measurements; ask your editor for your book's style sheet.
What to do in your book
- Pick a style and write it on your style sheet. For most nonfiction books, that is Chicago.
- Watch data-heavy chapters. In a passage full of figures, numerals are usually easier to read than a string of spelled-out numbers.
- Let dialogue sound natural. The CMOS Shop Talk post notes that narration and dialogue in a story or memoir do not have to follow every rule if readability suffers.
- Leave it to your copy editor to make numbers consistent across the whole book; see what a copy editor does.
For other style choices your editor will ask about, see the Oxford comma and that vs which.
Start here: search one chapter for numerals under 101 and numbers at the start of sentences. Fix those two, and most of your number style is done.
Common questions
What numbers should be spelled out?
In books following The Chicago Manual of Style, spell out whole numbers from zero through one hundred in general text, and use numerals above that. Spell out any number that starts a sentence. News writing (AP style) instead spells out only one through nine.
Should you spell out numbers at the start of a sentence?
Yes, in Chicago style. Chicago recommends spelling out a number that begins a sentence. If that is awkward ("Two thousand twenty-six was..."), rewrite the sentence so the number is not first.
What if a sentence has numbers above and below one hundred?
Chicago recommends using the same style for all the numbers in a sentence or paragraph that refer to the same kind of thing. "We interviewed 8 founders and 120 managers" uses numerals for both, because both count people.
Is it ten or 10 in a book?
In Chicago style, "ten." In AP style, used by most news outlets, "10." Most US book publishers follow Chicago.
Sources: CMOS Shop Talk (The Chicago Manual of Style's blog), Carol Saller, Numbers in Creative Writing (spell out zero through one hundred, CMOS 9.2; numbers at the start of a sentence, 9.5; consistency within a category, 9.7; readability over consistency; AP exceptions for years and number-letter expressions), read November 1, 2026. The AP one-through-nine convention is general knowledge of AP style. Examples and guidance were written by Scribe Media. Published by Scribe Media.