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
- Exception: “Use words for approximations of numbers of days, months, and years (e.g., about three months ago)” (p. 112).
C. Use words to express
D. Use words and numerals to express “back-to-back modifiers” (APA, 2010, p. 112) e.g., 2 four-way stops.
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.