When to Spell Out Numbers in Writing: APA, MLA, Chicago, and AP Style Rules

Numbers appear in almost every form of writing, and one of the most common questions writers face is when to spell them out and when to use digits. The answer depends on the style guide you're following and the type of writing you're doing. This guide covers the rules for academic writing (APA, MLA, Chicago), book writing (Chicago), and business writing (AP), with a comparison table, common exceptions, and worked examples for every case.

Spell Out Numbers Rules by Style Guide: Comparison Table

The four major style guides handle numbers differently. The table below summarizes the core rules so you can quickly find what your target style requires.

Individual style guides have exceptions and nuances that don't fit in a summary table. If you're writing for a specific journal, publisher, or institution, always check their author guidelines for style-specific requirements. Editor World's academic editors are familiar with each of these style guides and their common exceptions.

When to Spell Out Numbers in Academic Writing

Academic writing follows strict style guidelines, and the rules for numbers vary depending on which style guide your institution or journal requires. The three most commonly required in academic contexts are APA, MLA, and Chicago.

Under APA style, writers should spell out numbers below 10 and use digits for numbers 10 and above. So you would write "eight participants" but "76 respondents" and "4,813 survey responses." MLA follows a similar approach but frames the rule differently: numbers expressible in one or two words should be spelled out, so "eight" and "seventy-six" would be written as words, while "4,813" would appear as a numeral. Chicago style, commonly used in history and humanities, generally recommends spelling out numbers from one through one hundred, so both "eight" and "seventy-six" would be written out, while "4,813" would remain a numeral.

A few universal rules apply across most academic style guides. Always spell out a number that begins a sentence, regardless of its size. Never start a sentence with "4,813." Instead, rewrite the sentence so the number falls elsewhere, or spell it out fully. You should also be consistent throughout your document. If you use numerals for 76 in one section, don't switch to "seventy-six" in another.

When a sentence contains both small and large numbers, consistency usually takes priority over the standard spell-out rule. If two numbers in the same sentence refer to the same category of thing, they should be formatted the same way. For example, rather than writing "We surveyed eight schools and 76 universities," most academic style guides recommend "We surveyed 8 schools and 76 universities" so that both figures appear as numerals. The APA manual is explicit on this point, noting that when numbers must be compared or contrasted in the same sentence, numerals should be used throughout for consistency.

When to Spell Out Numbers in Book Writing

Fiction and narrative nonfiction follow somewhat different conventions than academic writing, and most publishers defer to the Chicago Manual of Style as the standard reference for book writing.

For books, the general rule is to spell out numbers that can be expressed in one or two words, and often numbers up to one hundred. "Eight" would always be written as a word in a novel, and "seventy-six" would typically be spelled out as well. However, a number like 4,813 would usually appear as a numeral because spelling it out ("four thousand eight hundred and thirteen") interrupts the flow of the prose and can feel cumbersome for readers.

Context matters. In dialogue, numbers are almost always spelled out to reflect the way people actually speak. A character would say "I counted seventy-six steps to the door" rather than "I counted 76 steps to the door." In descriptive or narrative passages, the same logic applies. Readability and rhythm should guide your decision.

When a sentence contains both small and large numbers in book writing, the approach is more flexible than in academic writing, but readability still guides the decision. If a sentence mixes a small number and a large one, writers often choose whichever format feels more natural in context. "The village had eight taverns and 4,813 residents" keeps "eight" spelled out because it reads smoothly, while "4,813" stays as a numeral because spelling it out would slow the reader down. However, if the two numbers refer to the same type of thing ("The army lost eight soldiers in the first battle and 76 in the second"), many editors recommend writing both as numerals for visual consistency.

One area where digits are preferred even in books is when dealing with large or highly specific numbers. A historical novel referencing a population of 4,813 people in a frontier town would keep that as a numeral to preserve clarity and precision.

When to Spell Out Numbers in Business Writing

Business writing prioritizes clarity and efficiency, and the conventions for numbers reflect that. Most business style guides, including those based on the Associated Press (AP) style, recommend spelling out numbers one through nine and using digits for 10 and above.

In a business report or professional email, you would write "eight clients" but "76 transactions" and "4,813 units sold." The goal is to make data easy to scan and comprehend quickly, which is why numerals are preferred for larger figures.

When a sentence contains both small and large numbers, AP style follows the same consistency principle as academic writing. If two numbers in the same sentence refer to the same category, use numerals for both, even if one falls below 10. Instead of "The company opened eight locations in the Northeast and 76 in the Southeast," AP style recommends "The company opened 8 locations in the Northeast and 76 in the Southeast." This keeps the sentence visually balanced and easier to read at a glance.

Numbers that begin a sentence should always be spelled out, so you would write "Seventy-six new accounts were opened in Q3" rather than starting with the numeral. In tables, charts, and data-heavy documents, numerals are almost always used regardless of size, since visual consistency is more important than stylistic convention in those contexts.

Exceptions: When to Always Use Digits

Some categories of numbers are almost always written as digits across every style guide, regardless of size. If you're unsure how to handle any of the following, digits are usually the safer choice.

• Currency. Use digits with the currency symbol: $8, €50, ¥1,000. Spelling out currency amounts ("eight dollars") is rare outside dialogue and legal writing.
• Percentages. APA and AP use the percent symbol with digits (8%). MLA and Chicago typically write out "percent" but keep the digit (8 percent).
• Dates. Digits for the day (March 5, not March fifth) and the year (2026, not twenty twenty-six).
• Times of day. Digits with a.m. and p.m. (7:30 a.m., not seven thirty a.m.).
• Ages. APA and AP use digits (an 8-year-old child). MLA and Chicago spell out simple ages (eight years old).
• Decimals. Always digits (0.5, 3.14, 8.75).
• Fractions in technical contexts. Digits (1/2, 3/4). In prose, fractions are often spelled out (one-half, three-quarters).
• Measurements with units. Digits (5 kg, 10 ml, 3 inches).
• Scores, ratios, and votes. Digits (a 5-3 vote, a 2-1 ratio, the score was 24-17).
• Statistical results. Digits (p = 0.05, n = 24, r = 0.72).
• Page and section numbers. Digits (page 5, Chapter 3, Section 2.1).
• Very large round numbers. Combined format (6 million, 4.5 billion) rather than 6,000,000 or four point five billion.

Common Number Mistakes Professional Editors See Most Often

Editor World editors have reviewed more than 100 million words of client writing across academic manuscripts, business documents, and book manuscripts. The number-related errors that appear most frequently are the same handful of mistakes:

• Starting a sentence with a digit. "4,813 respondents completed the survey" should be "A total of 4,813 respondents completed the survey" or "The survey was completed by 4,813 respondents."
• Inconsistent formatting for the same category. Writing "eight schools" and "76 schools" in the same paragraph. When numbers refer to the same thing, format them the same way.
• Mixing style guides across a single document. Applying APA rules in one section and Chicago rules in another. Commit to one style guide for the whole document.
• Ambiguous hyphenation with numbers as compound modifiers. "A 10 year old book" should be "a 10-year-old book" when it precedes a noun.
• Missing space between number and unit. "5kg" should be "5 kg" in most style guides, with a space between the number and the unit.
• Wrong dash between number ranges. "Pages 12-18" uses a hyphen where an en dash is required: "pages 12–18."
• Ordinal number formatting. "1st place" is acceptable in business and journalistic writing but not in most academic contexts, where "first place" is preferred.

These are the errors a professional human editor catches consistently. Grammar-check tools miss most of them, particularly the consistency issues that require reading across an entire document to spot.

A Quick Reference Summary

Knowing when to spell out numbers and when to use digits comes down to understanding your audience and the conventions of your field. Academic writers should follow their required style guide closely and prioritize consistency. Book writers should lean toward spelling out numbers for readability and natural flow. Business writers should default to numerals for larger figures and anything involving data, currency, or measurement.

When a sentence contains both small and large numbers referring to the same category, most style guides agree: use numerals for both to keep things consistent and clear. When in doubt, the safest rule across all three contexts is this: spell out numbers that are simple and small, use numerals for precision and larger figures, and never start a sentence with a digit.

Frequently Asked Questions

Get Expert Help With Style and Formatting

If you need expert review of number formatting, style guide consistency, or overall clarity before a submission deadline, Editor World's academic editing services, book editing services, and business document editing services connect you with native English editors who work in APA, MLA, Chicago, and AP style. Choose your own editor, request a free sample edit, and receive your document reviewed entirely by a qualified human editor with no AI used at any stage.

Page last reviewed: September 2026. Content reviewed by Debra F., PhD, Professional Editor. Editor World, founded in 2010 by Patti Fisher, PhD, is BBB A+ accredited with a 5.0 / 5 Google Reviews rating. Recommended by Boston University and other top institutions.