What are the APA Style rules regarding numbers?
The American Psychological Association’s (2010) Publication Manual of the American Psychological Association provides extensive information and examples on using numbers. This FAQ will focus on the basics, so please refer to the manual for more information.
A. General rule: “Use numerals to express numbers 10 and above and words to express numbers below 10” (American Psychological Association (APA), 2010, p. 111).
B. Use numerals to express numbers that
- are “in the abstract of a paper or in a graphical display of a paper” (p. 111); see "Feel Like a Number? A Tax Day Tribute" (Breitenbach, 2010a) for an explanation.
- “immediately precede a unit of measurement” (APA, 2010, p. 111) e.g., 2 cm.
- “represent statistical or mathematical functions, fractional or decimal quantities, percentages, ratios, and percentiles and quartiles” (p. 111) e.g., divided by 4, more than 2%.
- “represent time, dates, ages, scores and points on a scale, exact sums of money, and numerals as numerals” (p. 112).
- Exception: “Use words for approximations of numbers of days, months, and years (e.g., about three months ago)” (p. 112).
- “denote a specific place in a numbered series, parts of books and tables, and each number in a list of four or more numbers” (p. 112).
C. Use words to express
- “any number that begins a sentence, title or text heading. (Whenever possible, reword the sentence to avoid beginning with a number)” (p. 112).
- “common fractions” (p. 112) e.g., one third of the group.
- “universally accepted usage” (p. 112) e.g., the Ten Commandments; see "Feel Like a Number? Part 4. Numbers Expressed in Words" (Breitenbach, 2010b) for information.
D. Use words and numerals to express “back-to-back modifiers” (APA, 2010, p. 112) e.g., 2 four-way stops.
- Exception: If readability suffers, spell out both numbers e.g., “first two items” (p. 113), not “1st two items” (p. 113) or “first 2 items” (p. 113).
E. “Use commas between groups of three digits in most figures of 1,000 or more” (p. 114).
page numbers page 1029
binary digits 00110010
serial numbers 290466960
degrees of temperature 3071 F°
acoustic frequency designations 2000 Hz
degrees of freedom F(24, 1000). (p. 114)
F. “To form the plurals of numbers . . . add s or es alone, without an apostrophe” (p. 114) e.g., 1800s, sixes and sevens.
For more information on numbers, including more details on the information provided here as well as how to present ordinal numbers, decimal fractions, and Roman numerals, please see pages 111-114 in the APA manual.
American Psychological Association. (2010). Publication manual of the American Psychological Association (6th ed.). Washington, DC: Author.
Breitenbach, A. (2010a, April 15). Feel like a number? A tax day tribute [Blog post]. Retrieved from http://blog.apastyle.org/apastyle/2010/04/feel-like-a-number-a-tax-day-tribute.html
Breitenbach, A. (2010b, April 27). Feel like a number? Part 4. Numbers expressed in words [Blog post]. Retrieved from http://blog.apastyle.org/apastyle/2010/04/feel-like-a-number-part-4-numbers-expressed-in-words.html