Writing Numbers with Fractions and Fractions in Full

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Hyphens with Whole Numbers and Numbers with Fractions

Here are the rules for using hyphens with whole numbers and numbers that include fractions.

writing numbers with fractions
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Do Not Use Hyphens with Numbers Used as Quantifiers

When the number is a quantifier to a noun, do not use a hyphen. In these examples, the numbers are highlighted and the nouns are in bold.
  • The journey takes two hours.
  • The journey takes two and a half hours.
  • The journey takes twenty-three and a quarter hours.
    • (In this example, "twenty-three" is hyphenated because that's how 23 is written in full.)
  • The journey takes 23.25 hours.
  • The journey takes one and three-quarter hours.
    • (Here, "three-quarter" is hyphenated because that's how a fraction is written in full.)
It doesn't matter how complicated your number is, if it's a quantifier to a noun, then it is not hyphenated. When your number is a quantifier, the only hyphens are the ones that would be there ordinarily (e.g., in numbers such as "twenty-three," "three-quarter").

Use Hyphens with Numbers Used in Adjectives

When the number is the first part of a compound adjective, use hyphens to group the whole adjective together to show it is a single adjective. In these examples, the compound adjectives that include the numbers are highlighted and the nouns are in bold.
  • It is a two-hour journey.
  • It is a two-and-a-half-hour journey.
  • It is a twenty-three-and-a-quarter-hour journey.
  • It is a 23.25-hour journey.
  • It is a one-and-three-quarter-hour journey.
Again, it doesn't matter how complicated your number is, if it's the first half of a compound adjective, then it is hyphenated along with the rest of the adjective. Remember that you group an adjective with hyphens to show it's a single grammatical unit (i.e., a single, albeit multi-word, adjective).

Read more about compound adjectives.

Hyphenating Terms with the Word "Year"

Writers often ask about hyphenation with terms that include "year." Here are the rules:

Hyphenate All the Words in a Compound Noun with Years

The term "two-year-old" is a multi-word noun (called a compound noun.) Here are some more examples of compound nouns with the term "year old" (the compound nouns are highlighted).
  • A two-year-old knows its mind.
  • There are three two-year-olds in the group.
  • A four-and-a-half-year-old knows its mind.
  • There are three four-and-a-half-year-olds in the group.
This time, there are hyphens to show that the compound noun is a single grammatical unit (i.e., a single, albeit multi-word, noun). It can happen with other words too:
  • He claims to have seen a six-and-a-half-footer near the breakwater.
Read more about compound nouns. Remember that there are no hyphens when the number is used as a quantifier, and this includes when the number quantifies the noun "year." In these examples, the numbers are highlighted and the nouns are in bold:
  • She studied for four years.
  • She studied for four and a half years.
Remember, too, that numbers used in compound adjectives are hyphenated, and this includes when the compound adjective includes the word "year." In these examples, the compound adjectives are highlighted and the nouns are in bold:
  • She studied for a four-year period.
  • She studied for a four-and-a-half-year period.

Writing Fractions in Words

writing fractions in full word form

The most common convention when writing fractions in word form is to write the top number (the numerator) as a cardinal number (e.g., three, four, five) and the bottom number like an ordinal number (thirds, fourths, fifths). For example:
  • The population reduced by two-fifths.
    • (This is how ⅖ is written.)
  • The population reduced by one-half.
    • (This is how ½ is written.)
  • The population reduced by 3 and one-third.
    • (This is how 3⅓ is written.)
When the numerator or the denominator includes a hyphen in its own right (e.g, twenty-three or twenty-thirds), then the hyphen joining the numerator and the denominator is often dropped for style purposes. For example:
  • I will receive three thirty-fifths of my salary.
    • (This is how 3/35 is written. "Three-thirty-fifths" looks too unwieldy.)
  • I will receive forty-one fiftieths of my salary.
    • (This is how 41/50 is written. "Forty-one-fiftieths" looks too unwieldy.)
  • I will receive forty-fiftieths of my salary.
    • (This is how 40/50 is written. If there are no hyphens in the numerator or the denominator, then revert to the normal rules.)

Hyphenation with Fractions as Quantifiers

Another popular style differentiates between standalone fractions and fractions used as quantifiers. In this style, a fraction is not hyphenated when it stands alone but is hyphenated when it is used as a quantifier. For example:
  • The population reduced by two fifths.
    • (Note that this is different from the most common style shown above.)
  • There was a two-fifths reduction in the population.
    • (In this example, "two-fifths" is hyphenated because it quantifies "reduction.")
What convention should I use?

If you've come here looking for an answer on whether to hyphenate a fraction, here's your answer: It depends what convention your institution is using.

If you can't find any examples from your institution, then adopt the most common convention (i.e. the one that hyphenates fractions) and be consistent.

Why should I adopt the common convention?
  • Hyphenating a fraction makes it stand out as one grammatical unit, meaning it will not hinder reading flow.
  • "Two-thirds" counts as one word. "Two thirds" counts as two. So, hyphenating could be a way to reduce your word-count.
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See Also

What are adjectives? What are compound adjectives? Hyphens in compound adjectives How to write numbers in full Starting sentences with numbers