Four p.m. or 4 p.m.? 1950s or 1950’s? Writing an essay or paper can be challenging enough. Start to consider the various formatting rules that exist for including numbers in your essay, and you might find yourself overwhelmed by the conventions of writing. Fortunately, these rules are actually fairly straightforward and easy to remember. Review and practice them and they’ll soon become second nature, allowing you to spend less time thinking about guidelines and more time thinking about your writing.
When writing numbers in your essay, the general rule is that whole numbers below 10 should always be spelled out. You would assert that there are "three cars" or "eight baseballs." Numbers 10 and above should be written in numeral form: "21 bugs," "52 cards." When a number below 10 is grouped with a number above 10, the rule for the higher number takes precedence: "8 to 12 weeks."
Exact statistical measures, such as percentages, decimals, and mathematical operations, should always be written in numeral form. For example, “The success rate is 8%,” “Fill 5.5 cartons,” or “Divide the answer by 2.”
Use numerals for dates, times, and ages. For example, "October 27, 1986," "4 p.m.," or "37 years old." Spell out the number when writing out a time, such as "eleven o'clock."
Identification numbers should be written as numerals: "Room 7," District 4," "Channel 22."
Write years and decades in numeral form. Something might take place in 2005 or in the 1990s (decades do not use an apostrophe before the "s"). Centuries can be spelled out ("fifteenth century") or written in numeral form ("18th century").
Beginning of Sentence
Numbers that begin a sentence should always be spelled out: "Sixty-seven movies were released last month." However, for prose purposes, avoid using numbers at the beginning of sentences.
Spell out rounded or inexact numbers. Also spell out common fractions. You might say there were "about a thousand" people at a gathering, or that "one-quarter of the audience found it funny."