When to Hyphenate Numbers
  • 3-minute read
  • 19th February 2020

When to Hyphenate Numbers

We’ve written about hyphens and numbers before, but here we’re combining the two. Why? Because it isn’t always clear when a number needs a hyphen. However, the two main occasions to hyphenate numbers are:

  • When writing out compound numbers as words.
  • When using a number as part of an adjective.

Read on to find out when to hyphenate numbers in your writing.

Compound Numbers (21–99)

Always hyphenate the numbers 21 to 99 when writing them out as words:

I have twenty-one pairs of novelty socks.

My grandma is sixty-seven years old.

I have ninety-nine problems, but none involve a female dog.

Do the same when writing an ordinal version of one of these numbers:

My forty-first birthday was the best day ever.

And when writing a larger number that contains one of these numbers:

I ate one hundred and twenty-two burgers in 2019.

Around twenty-four million people eat fast food every day.

Where applicable, you can also omit the “and” when writing out larger numbers if preferred:

I ate one hundred twenty-two burgers in 2019.

However, it’s only 21 to 99 that we hyphenate in these large numbers. Larger round numbers, such as “one hundred,” do not require a hyphen.

Compound Adjectives

Always hyphenate adjectives that include a number when they appear in front of the noun they’re modifying. This applies to both words and numerals:

A six-foot ladder will be tall enough.

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We study seventeenth-century manuscripts.

I will send a 40-page document later today.

The 7-year-old boy lost his whistle.

However, these numbers don’t need a hyphen when they occur elsewhere:

The ladder is six feet tall.

The document comprises 40 pages.

Keep in mind, too, that some style guides suggest omitting the hyphen when a unit of measurement is abbreviated. For example, if you were using the Chicago Manual of Style, you would hyphenate an adjectival measurement when writing the unit out in full, but not when abbreviating it:

A six-foot ladder will be tall enough.

A 6 ft. ladder will be tall enough.

The same rules apply when writing out fractions. As a result, we hyphenate them when they’re used adjectivally in front of a noun, but not in other cases:

A two-third majority voted for the new laws.

He ate two thirds of the cake.

This same convention applies to other compound adjectives, too.

Summary: When to Hyphenate Numbers

Rules can vary on when to hyphenate numbers, so it is always worth checking your style sheet if you or your employer has one (or if you have been asked to use a standard style guide, like APA or Chicago). However, there are two occasions when it is standard to hyphenate a number:

  • When writing out 21 to 99 as words (e.g., twenty-one, ninety-nine).
  • When a number is part of an adjective (e.g., a seven-year-old boy).

And if you’d like an expert editor to check you’ve used numbers correctly in writing, why not submit a document for proofreading today? We’ll help you achieve perfect punctuation every time!

Comments (25)
Alex
13th November 2020 at 02:07
What about a hyphenated compound like this... do you insert hyphens between all of the numbers?: He climbed a two thousand five hundred foot mountain. OR: He climbed a two-thousand-five-hundred-foot moutain.
    Proofed
    13th November 2020 at 13:59
    Hi, Alex. The simple answer is that usually you would write larger numbers with numerals to ensure clarity (i.e., "a 2500-foot mountain"). Assuming that isn't an option, though, we would probably recommend "a two thousand five hundred-foot moutain" since "two thousand five hundred" would not itself usually be hyphenated (i.e., the hyphen connects the number and the measurement in the adjectival form, but you don't need to add extra hyphens to the number). However, as long as your meaning is clear, this is largely a matter of stylistic preference.
Andrea Walker
13th November 2020 at 18:43
How do you hyphenate a phrase such as "8-10 hour week"? Is it as written or "8-10-hour week"? The latter looks funny, but I think it follows the rule to hyphenate.
    Proofed
    14th November 2020 at 12:54
    Hi, Andrea. Clarity is the main factor here, so we'd avoid “8-10-hour week” since it could be a bit confusing (i.e., you have two hyphens doing different things: one indicating a range of figures; the other forming a compound). But you have plenty of options otherwise, including: 8-10 hour week 8–10 hour week (with an en dash rather than a hyphen, which is the correct punctuation mark for more formal writing) 8 to 10-hour week (where we use "to" instead of a hyphen or dash to indicate the range) In essence, while it is standard to hyphenate numbers used adjectivally, clarity always comes first!
      Brenda F
      16th February 2022 at 01:07
      I would have said here: 8- to 10-hour week. (You do not need an en dash here, which is Alt+0150, because the "to" is used for the range. The hyphen after 8 just means it goes along with hour as well, like the 10-hour week.)
      Proofed
      16th February 2022 at 09:49
      Hi, Brenda. "8- to 10-hour week" would certainly be a good option here. Another option that maintains the formal punctuation would be "8–10-hour week," with the en dash to indicate the range and the hyphen to indicate the compound adjective. But clarity is still the most important thing in most cases, so "to" is probably easier to follow for most people.
Arlinda Bush
2nd March 2021 at 17:54
When you are putting the year 2021 in an announcement wording for the date. Do you write it like Two thousand twenty-one or Two thousand twenty one? I understand the hyphen in compound numbers starting with 21 but to me this could go either way. I look forward to your reply
    Proofed
    3rd March 2021 at 09:24
    Hi, Arlinda. You wouldn't usually write out a year as words, so we'd suggest sticking with "2021" in that context. If you were writing out the year, though, you could use "twenty twenty-one" or "two thousand twenty-one" (it is only the "twenty-one" you need to hyphenate in any case).
Ashley Sides Johnson
3rd March 2021 at 04:04
I'm sending massive props to the person that managed to use Jay-Z's song, 99 Problems, as an example for when/how to hyphenate numbers!!!! (The example appears in this article.) I write web copy for a major health system and you may be my copy-writing soulmate!!! Hilarious.
    Proofed
    3rd March 2021 at 09:10
    Thank you! We're happy to take song requests for use in future illustrative examples, too.
Val
15th May 2021 at 01:05
Hi, which one is better? The company spent twenty trillion dollars. The company spent twenty-trillion dollars.
    Proofed
    19th May 2021 at 09:43
    Hi, Val. There's not usually any need to hyphenate larger numbers unless, as mentioned in this post, they contain a number between 21 and 99. So, it would be "The company spent twenty trillion dollars," but also "The company spent twenty-two trillion dollars."
Grant Writer
15th June 2021 at 21:58
39-year history or 39 year history?
    Proofed
    16th June 2021 at 08:49
    In that case, "39-year" is modifying "history," so you need the hyphen.
Steve Carrola
16th November 2021 at 22:06
Grammarly.com suggests "thirty-four-foot utility pole" but other sites suggest that "thirty-four foot utility pole" is more proper.
    Proofed
    17th November 2021 at 10:18
    Hi, Steve. "Thirty-four-foot utility pole" would be correct according to most modern style guides as "thirty-four-foot" is a single term modifying "utility pole." Hope that helps.
Philip
26th November 2021 at 13:17
Hi, could you help me with the following sentence please. The world's tallest arch, it was a six hundred and thirty foot, stainless-steel monument, built as a gateway to The West. I'm not sure if hyphens go between numbers used as adjectives that precede another adjective. I'm also unsure about hyphenating stainless-steel. Thank you
    Proofed
    26th November 2021 at 15:58
    Hi, Philip. Typically, you would still need to hyphenate an adjectival number in that situation. You can also hyphenate "stainless steel" if preferred, although it is a common enough term and unlikely to be misunderstood, so the hyphen is optional there. It might be worth noting that most style guides suggest using numerals rather than words for larger numbers (i.e., in this case, "630" rather than "six hundred and thirty"). And you typically only need a comma between adjectives when they are coordinate (i.e., they modify a word in a similar way), so it wouldn't be strictly necessary there. As such, I would possibly suggest writing "The world’s tallest arch, it was a 630-foot stainless steel monument, built as a gateway to The West." But if you prefer to write the number out in full, I'd probably suggest hyphenating the entire number and unit of measurement to clearly indicate that it is a single modifier. That would leave you with "The world’s tallest arch, it was a six-hundred-and-thirty-foot stainless steel monument, built as a gateway to The West." Ultimately, though, clarity of meaning and readability are the most important factors with hyphenation. So as long as it is clear in context what you mean (and you're not following a specific style guide), there's probably room for some flexibility here.
      Philip
      27th November 2021 at 12:17
      Much appreciated, thank you. I will keep you in mind when I'm ready to have the book proofread!
Beth Jones
27th April 2022 at 01:19
How would you write this scenario? "your proposal to construct one-hundred three- and four-bedroom homes was approved."
    Proofed
    27th April 2022 at 08:18
    Hi, Beth. Assuming you want to write all numbers out in full, the correct form would be “Your proposal to construct one hundred three- and four-bedroom homes was approved” (i.e., you don't need a hyphen in "one hundred"). However, unless you're following a style guide that specifies writing out all numbers in full, I would probably suggest writing "one hundred" as numerals instead. This will help to distinguish it from the numbers that follow: i.e., “Your proposal to construct 100 three- and four-bedroom homes was approved.”
Becky Helzer
29th April 2022 at 17:37
Hello! Could you give me some guidance on whether to hyphenate such things as "a 240-cc motorcycle engine" and "a 2-Ah battery"? Wondering if the hyphen is necessary between the numeral and the unit of measurement and if there's a reference I can use to support this. Thank you!
    Proofed
    30th April 2022 at 08:55
    Hi, Becky. Style guides vary on whether to hyphenate numbers and abbreviated units of measurement used adjectivally. Most will recommend hyphenating when a unit of measurement is spelled out in full (e.g., "a ten-foot ladder"). But it varies more when units are abbreviated. The Chicago Manual of Style, for example, says that "hyphens are never used between the numeral and the abbreviation or symbol, even when they are in adjectival form" (e.g., Chicago style would recommend "a 10 ft. ladder"). But the AMA Manual of Style and APA Publication Manual, by comparison, both say to hyphenate a compound in which a number is the first element and the compound precedes the noun it modifies regardless of whether the unit of measurement is abbreviated (e.g., they would recommend saying "a 10-ft ladder"). As such, the answer to your question may depend on whether you're using a particular style guide. If not, either approach is probably fine as long as the meaning is clear in context and you apply a consistent punctuation style to all similar compound modifiers in your writing. Hope that helps!
katelyn
22nd June 2022 at 18:47
Hi, Would it be correct to write "four or five-year term" or "four- or five-year term"? Thanks!
    Proofed
    23rd June 2022 at 09:59
    Hi, Katelyn. The correct form there would be “four- or five-year term.” The key factor is that you're essentially forming two compound modifiers (i.e., you're saying "four-year or five-year term”) but omitting the second term in the first case to prevent repetition. However, even when omitting "year" in the first case, you need to include a hyphen to show that "four" is intended as part of a compound (something known as a "suspended hyphen"). Hope that helps!

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