As with several other English grammar rules (capitalization of titles, we're looking at you!) relating to how to write numbers will vary depending on the sources you use. For example, in AP style, you would spell out whole numbers up to (and including) nine but write the numerals for 10 and above. In Chicago style, you would spell out whole numbers up to (and including) one hundred but write the numerals for 101 and above. Alternatively, you can spell out whole numbers up to (and including) nine and use numerals for the rest.
So, is there a way to remember the rules without having to consult a style book each time? Yes, but it depends on the nature of your writing and for whom you are writing. For example, if you are writing a dissertation that follows a particular style, it is best to consult the style book when any number comes up in the text. However, for general business writing, fiction and most nonfiction (unless it's technical writing), there are some standard rules to follow, which we will cover here.
Spell out whole numbers up to and including nine.
Spell out numbers that begin a sentence unless it is a year. When doing so, avoid using "and" such as "One hundred and one Dalmatians."
- 1975 was a great year for music.
- One thousand dollars is a lot of money to pay for that watch.
- One hundred one Dalmatians.
When you have multiple numbers within the same sentence, consistency is key if the items are in the same category. If the items are in different categories, use numerals for one category and spell out the other.
- She bought the car that seats five instead of the minivan that seats nine.
- I read four books with over 300 pages each and two articles that were 12 pages each.
When numbers are next to each other in the sentence, it is best to write out one and use a numeral for the other in order to differentiate them.
- We bought four 7-inch frames.