How to Write Numbers in APA Style

Style guidelines from the American Psychological Association (APA) help writers maintain a uniform way of writing. Because APA style is used for scientific and clinical writing, numbers are often included. Readers can more easily understand information when it is consistently communicated in one way. Many APA rules also help save space because the rules seek to increase clarity in presentation.

The most common and frequently used rule for writing numbers in APA style is determined by whether the number is under 10. All numbers below 10 should be written out in word form. For example, numbers like four or seven. Numbers 10 and above are written as a numeral like 10, 17 and 233. One of the exceptions to this rule is when a sentence starts with a number. In this case, the number is always written out as a word. For example, "Fifteen students were sick; two teachers went home." To avoid confusion and preserve consistency when writing numbers in APA style, try to avoid starting a sentence with a number.

Another exception to writing out numbers under 10 is when writing a specific measurement, amount, date, age or money. In this case, the number should be written as a numeral: 8 miles, 4 cents, a 7-year-old boy, 6 weeks ago, 3 hours before dinner and a $2 fine. Finally, in APA style consistency in presentation is key even if it means bending the rules. For example, you would write "6 out of 10 dentists preferred the last treatment" instead of "six out of 10."

A commonly used number rule in APA style is to write out fractions as words. For example, write "half" instead of 1/2. But, if a fraction is unusual, such as 3/16, then use the numeral form. For decimal usage, always place a "0" before the decimal: 0.91, for example. And finally, when writing about percentages, always use a numeral, even if the number is less than 10. For example: 7% of people surveyed did not respond to the question. APA rule 4.31 also stipulates using "numerals to express numbers that represent time, dates, ages, scores and points on a scale, exact sums of money and numerals as numerals." The same rule continues on to state the exception of using words for approximations of numbers when words like "almost" or "about" precede the number. Symbols like % and $ are used in APA style when they are preceded by a number that is not spelled out as a word and especially in charts and graphs to preserve space.