Even outside of math class, numbers show up everywhere, including in writing. However, unlike in math class, sometimes numbers need to be written out. For many writers, when to spell out numbers and when to write the numbers as numerals are quite confusing. Just like many other grammatical concepts in the English language, there are rules concerning when to write out numbers. Here we will discuss when to spell out numbers and when not to.
When to Spell Out Numbers
Rule 1: Numbers under 10
Example: The cat captured three mice.
Rule 2: Beginning of a sentence
Example: Thirty days is a length of time equal to approximately one month.
Rule 3: Fractions, except mixed fractions
Example: Approximately one-half of all voting eligible citizens do not vote in November.
Rule 4: Time, except when using the terms A.M. or P.M.
Example: The class ends at three o’clock.
Rule 5: Short sentences involving numbers
Example: She made forty dollars.
When to Use Numerals
Rule 1: Numbers above 10
Example: There are 12 eggs in a dozen.
Rule 2: Dates and years
Example: The last day of school is May 3, 2015.
Rule 3: Mixed fractions
Example: The recipe requires 1 ½ cups of sugar.
Rule 4: Time using A.M. or PM.
Example: The class begins at 8:00 A.M.
Rule 5: Percentages
Example: The governor won the election with 54% of the popular vote.
Rule 6: Decimals
Example: The ship’s armor is only 0.5 meters thick at the waterline.
Tips for Both Numbers and Numerals
When in doubt, spell out the number rather than writing the numeral.
Decades can be written either way. For example, “the economy grew in the 90’s” and “the economy grew in the nineties” are both correct.
When writing a recipe, do not spell out numbers and instead just use numerals.
If a number is rounded or an estimate, spell it out. For example, "about 50 hundred people died in that horrible disaster."
If there are two numbers adjacent to each other, spell out the number that has the fewest letters, such as five 25-year-old girls.
When using a given rule that can go either way (writing out a number versus leaving it as a numeral), remember to stay consistent in the whole article.