The Chicago Manual of Style lays out the following rules for spelling out numbers: Spell out numbers zero through one hundred Use numerals for numbers over one hundred Spell out certain round numerals, specifically: whole numbers one through one hundred followed by hundred, thousand, or hundred thousand), except in monetary amounts or percents Examples: Seventy-two One thousand Two hundred thousand Seventy thousand Two hundred 72 percent 101 Additionally, when two numbers need to be placed next to each other, it’s best to spell out one of them (usually the smaller amount). Example: 10 nine-inch boards three 12-foot waves Additionally, when numbers are used to start a sentence, they should always be spelled out. Twenty-four thousand applications were submitted in 2018. When to Write Out Numbers: What Chicago, APA, and MLA Say About Numerals
