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Numbers in APA style aren’t just about picking digits or words based on the vibe and hoping for the best. There’s a real system at work, and once you learn it, APA number formatting is fairly logical.
Here are the eight rules that cover the situations you’ll encounter most often:
1. Spell out numbers zero through nine
The most fundamental APA rule when it comes to numbers: if a number is between zero and nine and isn’t a measurement, write it out in words. So, you’d write “three participants” and “nine trials,” not 3 and 9.
2. Use numerals for 10 and above
Once you hit double digits, switch to numbers. Write 10, 25, 100 – not ten, twenty-five, one hundred. Piece of cake.
3. Always use numerals for measurements
Measurements always get numerals, no matter how small. That includes time, distance, weight, age, money, and statistics. It’s 5 minutes, 3 kg, and 2 years old, even though those numbers fall below 10.
4. Spell out numbers at the beginning of a sentence
Never start a sentence with a numeral. If rewriting the sentence isn’t an option, spell the number out. “Forty-two students completed the survey” – not “42 students completed the survey.”
Pro tip: restructuring the sentence will usually look cleaner in your paper.
5. Use numerals for exact numbers in a series that includes a value of 10 or more
When you’re listing numbers in a series that includes values of 10 or more, use numerals for all of them, even the ones below 10. Consistency is key here. For example: “Groups had 3, 7, and 14 participants.”
6. Spell out common fractions and widely known expressions
Common fractions used in general (non-measurement) contexts get spelled out: one-third of respondents, a two-thirds majority. The same goes for expressions like the Fifth Amendment or the Seven Deadly Sins, since those are phrases and not quantities.
7. Use numerals for decimals, percentages, and statistical values
Statistical reporting lives in numeral territory, always. Write 0.05, 95%, p<.001. Even if the value is less than 10, the measurement rule kicks in, and numerals win out.
8. Spell out ordinals below 10 (unless they’re measurements)
Ordinals follow the same basic logic as cardinals: spell out first through ninth, use numerals for 10th and above. So it would be “the third hypothesis” but “the 12th experiment.”
Quick reference: Words vs. numbers
The bigger picture
APA’s number rules exist to make research papers easier to read and scan, especially when your reader is bouncing between stats, sample sizes, and citations. Once these eight rules become second nature, you’ll spend a lot less time second-guessing yourself mid-paragraph.
Frequently Asked Questions
Does APA style spell out numbers under 10?
Yes. APA 7th edition spells out numbers zero through nine when they appear as general quantities. That said, numbers below 10 that represent measurements, statistics, or data points always use numerals regardless of size.
When do you use numerals instead of words in APA?
Use numerals for 10 and above, all measurements (time, age, weight, distance), decimals, percentages, statistical values, and any number that falls in a series that includes values of 10 or more.
What are the APA rules for numbers at the start of a sentence?
APA says sentences should never begin with a numeral. Either rewrite the sentence so the number falls elsewhere, or spell the number out at the start of the sentence.
Do ordinal numbers follow the same rules in APA?
Yes. Spell out first through ninth in non-measurement contexts, and use numerals for 10th and above. If an ordinal is used as a measurement, use a numeral regardless: “scored in the 3rd percentile.”
