In today’s statistics-conscious world, many documents contain numbers. Here are some guidelines for dealing with them.
In general, write out numbers one through nine. Use numerals for numbers above “9.”
Write out a number if it starts the sentence. “Twenty people attended the lecture.”
If the number would be cumbersome, edit the sentence. For example, instead of saying that “fifty-seven people reported this and that” you can say that “more than 50 people reported this and that.”
The one exception to this rule is if the sentence begins with a year. “2013 has been a very interesting year” is correct.
Spell out casual expressions, such as “thanks a million.”
In most cases, use decimals instead of fractions.
If you use fractions, spell out amounts less than one and hyphenate the words (e.g., “four-fifths”). For amounts greater than one, use numerals (e.g., 5 ½).
Use a dollar sign and decimals when writing amounts $1 and above. Generally use words to denote large amounts (e.g., $5 million).
Use decimal figures (not fractions) for percentages (e.g., 75 percent). Put a “0” before any amount less than “1” (e.g., 0.75 percent).
For more information, consult The Associated Press Stylebook.