Hyphenation with Numbers and Units of Measure



Few punctuation marks prompt as much debate and discussion about when and where to place them as the hyphen does.

Opinions and directives vary. GrammarBook.com aims to help define common written English that applies proper, generally accepted rules. Those guidelines likewise look to reinforce a precise and articulate use of the language.

This means our guidance for our current hyphen topic may differ from the recommendations you may find in research and scientific stylebooks.

An issue that still challenges many writers concerns the use and placement of hyphens with numbers and units of measure. For example, which of the following are correct?

50-ft. yacht
80 lb. bag
six centimeter caterpillar
100-meter dash

In addressing this topic, we side closer to the 16th edition of The Chicago Manual of Style. CMOS’s stance can be a bit confusing at times; we hope to clarify it in this article.

According to CMOS, “if an abbreviation or a symbol is used for the unit of measure, the quantity is always expressed by a numeral. Such usage is standard in mathematical, statistical, technical, or scientific text, where physical quantities and units of time are expressed in numerals, whether whole numbers or fractions, and almost always followed by an abbreviated form of the unit … Note that hyphens are never used between the numeral and the abbreviation or symbol, even when they are in adjectival form.”

Correct:

50 ft. yacht
80 lb. bag
6 cm caterpillar
100 m dash (Note that CMOS uses a period when abbreviating English units but not when abbreviating metric units.)

CMOS further advises using a hyphen when the unit, abbreviation, or symbol is spelled out, with the exception of percent.

Correct:

50-foot yacht
80-pound bag
six-centimeter caterpillar (Note that we spelled the number here because it’s less than ten and not used with a symbol or abbreviation.)
100-meter dash

But

10 percent raise

Written English in specialized fields such as healthcare, education, and science often adheres to its own specific stylebook. In those cases, the stylebook should serve as the writer’s guiding authority.

 

Pop Quiz

Correct the following sentences if needed. The answers appear below.

1. She served the drinks in 16 ounce mugs.

2. She served the drinks in 16-oz mugs.

3. The mugs could hold up to 16-ounces.

4. Weather predictions are about 50-percent accurate.

5. The 621-gram diamond is the largest in the world.

6. The 621-g. diamond is the largest in the world.

 

Pop Quiz Answers

1. She served the drinks in 16-ounce mugs. [use a hyphen when the unit is spelled out]

2. She served the drinks in 16 oz. mugs. [Hyphens are never used between the numeral and abbreviation, even when in adjectival form. Use a period when abbreviating English units.]

3. The mugs could hold up to 16 ounces. [no hyphen as “16 ounces” is not used as an adjective here]

4. Weather predictions are about 50 percent accurate. [hyphens are not used with percent]

5. The 621-gram diamond is the largest in the world. CORRECT

6. The 621 g diamond is the largest in the world. [Hyphens are never used between the numeral and abbreviation, even when in adjectival form. A period is not used when abbreviating metric units.]

Posted on Wednesday, February 22, 2017, at 7:21 pm

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37 Comments on Hyphenation with Numbers and Units of Measure

37 responses to “Hyphenation with Numbers and Units of Measure”

  1. Bill T. says:

    Magnificent, I will apply this to my writings.

  2. Steven A. says:

    This is very helpful for developing my writing skills in my college classes. Thank you so much for all this information.

  3. David B. says:

    Interesting discussion.

    Should “… generally accepted rules” be written …generally-accepted rules?

    Thanks for the great columns.

  4. Nick G. says:

    Hello – I saw your section on hyphens. I cannot recast the following. I was wondering whether it was punctuated correctly. I didn’t use suspended hyphens. Thank you very much.

    a 15%-to-20%-a-year reduction in profits
    a 20%-a-year reduction
    a 20%-per-year reduction

    a 15-to-20-percent-a-year reduction in profits

    a $2-million-to-$5-million-a-year baseball contract
    a $5-million-a-year contract

    a $35,000-to-$45,000-per-year position

    Correctly to all punctuation above with the hyphenage?

    Thank you very, very much.

    • We recommend that you write:

      a 15% to 20% per year reduction in profits (we recommend using the more formal “per year” over “a year,” the latter being a term that is sometimes associated with only one year) OR
      a 15%–20% per year reduction in profits (Note that we have used an en dash to be consistent with most publishers when designating a range. You may also use a hyphen: a $1-$5 per day surcharge.)

      a 20% per year reduction

      a 15 to 20 percent per year reduction in profits

      a $2 million to $5 million per year baseball contract OR
      a $2 million–$5 million per year baseball contract
      a $5 million per year contract

      a $35,000 to $45,000 per year position OR
      a $35,000–$45,000 per year position

  5. Kelly F. says:

    Without recasting the examples below, are they very technically correctly punctuated with the hyphens as I have them?

    a $1-to-$5-a-day surcharge
    a $10-to-$20-per-barrel price
    an $80-million-to-$90-million-a-year industry
    a 10-to-15-percent-a-year increase
    a 10%-to-15%-a-year increase
    65-to-85-cent-a-week raises
    a group of 20-to-30-year-old men

    Deepest thanks.

    • We recommend that you write:

      a $1 to $5 per day surcharge (we recommend using the more formal “per day” over “a day,” the latter being a term that is sometimes associated with only one day) OR
      a $1–$5 per day surcharge (Note that we have used an en dash to be consistent with most publishers when designating a range. You may also use a hyphen: a $1-$5 per day surcharge.)
      a $10 to $20 per barrel price OR a $10–$20 per barrel price
      an $80 million to $90 million per year industry OR an $80 million–$90 million per year industry
      a 10 to 15 percent per year increase
      a 10% to 15% per year increase OR a 10%–15% per year increase
      65- to 85-cent per week raises
      a group of 20- to 30-year-old men (note the use of the suspended hyphen in these final two examples)

      • Tina R. says:

        Isn’t this example flawed in terms of punctuation?

        65- to 85-cent per week raises

        Shouldn’t it be

        65- to 85-cent-per-week raises

        Thank you.

  6. Joseph Londino says:

    The comment is about the use of periods with abbreviations. In todays email the unit for pound, lb, was used with a period-lb. This example is the only correct use of a period with an abbreviation for a unit of measure, the abbreviation is at the end of a sentence.
    There are standard rules for abbreviations in science:
    1) a period is NEVER used except as in the example above.
    2)A unit abbreviation is capitalized only if it refers to a proper noun: N, Btu, J for newtons, british thermal unit, and joule. Notice also that when the noun refers to the unit it is not capitalized.
    3) There is never an ‘s’ used after a unit. For example ‘ft’ is used for feet or foot.

    • As we state in the article, “our guidance … may differ from the recommendations you may find in research and scientific stylebooks.” We also noted that the Chicago Manual of Style “uses a period when abbreviating English units but not when abbreviating metric units.”

  7. S. G. says:

    I believe that with the examples below I don’t need to use commas between any of the elements (in all examples) because the numerals stand out and the examples are crystal clear without them. Do you concur with the punctuation in Set 1?

    SET 1
    a 2-hour 11-minute 42-second finish time
    a 2-hour 11-minute and 42-second finish time
    a 3-year 9-month 17-day project
    …lasted 3 years 9 months 17 days.
    …lasted 3 years 9 months and 17 days.

    But if we spell them out, I believe we need commas for clarity:

    SET 2
    a two-hour, eleven-minute, forty-two-second finish time

    …lasted two hours, eleven minutes, and forty-two seconds.

    • While we were not able to find specific guidance on this situation in The Chicago Manual of Style, we do note that The Associated Press Stylebook (AP) would use commas and would express the times in numerals. For clarity, we recommend using commas whether the times are expressed in numerals or spelled out. For sports statistics, AP recommends: a finish time of 2:11:42.

  8. Kelly F. says:

    But if I opted to use ‘a year’ instead of ‘per year,’ would it still be treated the same, minus the hyphens? Good, technically speaking, to all below?

    an $80 million to $90 million a year industry

    an $80 million–$90 million a year industry

    an $11 a barrel price
    an $11 per barrel price

    a $10–$15 per barrel price
    a $10–$15 a barrel price

    a $2 million to $4 million per quarter loss

    a $2 million–$4 million per quarter loss

    a $5 million per quarter loss

    a $5 million a quarter loss

    • In followup to our response of February 25, 2017, we strongly recommend that “per” be favored over “a” in these constructions in order to ensure clarity and avoid miscommunication. Per is the cleaner word by definition. A phrase such as a $5 million a quarter loss lacks clarity to us, especially in such a weighty matter as whether $5 million is being lost each quarter or in a specific quarter. If you insist in using “a,” we recommend using hyphens in these constructions to assist in clearer reading and cleaner copy:

      an $80 million to $90 million-a-year industry
      an $80 million–$90 million-a-year industry
      an $11-a-barrel price
      a $10–$15-a-barrel price
      a $5 million-a-quarter loss
      .

  9. Kelly F. says:

    Can we drop the word ‘million’ after the first number?

    Instead of:
    ‘an $80 million–$90 million per year industry,’

    Could we tighten it up and use
    ‘an $80–$90 million per year industry’?

    • Writing an $80-$90 million per year industry is too open to misinterpretation. While perhaps unlikely in this particular case, this type of construction in general could be misinterpreted as an industry ranging from 80 dollars to 90 million dollars. The AP Stylebook specifically recommends the form “$80 million to $90 million.”

  10. Lauren says:

    Is it better to write “..who is 80+ years,…” or “..who is over 80-years old…”
    Is there ever a time when using “+” is applicable?

    • We do not recommend using the mathematical plus sign in that manner in formal writing. You could write either “who is 80-plus years old” or “who is over 80 years old.” The phrase “who is over 80 years old” does not use a hyphen. Please see our post Hyphens with Numbers for more information.

  11. Lou Guillou says:

    I got the correct answer for “There are one thousand four hundred twenty pages in the book.”

    However, contrary to what grammar books say about it, I still think
    “There are one-thousand four-hundred twenty pages in the book.” is better.

    Can you give a reason (other than “grammar books say so”) why my preference is undesirable?

    • As described in our post Numbers as Adjectives, you would hyphenate when a number is used with another word to form a compound adjective before a noun, that is, when they describe another object. An example would be “a one-thousand-four-hundred-twenty-page book.” In your example sentence, the numbers one thousand and four hundred are numbers that are not hyphenated. All compound numbers from twenty-one through ninety-nine are hyphenated. Also see our Rules for Writing Numbers.

  12. Tina R. says:

    Instead of using suspended hyphenation, would you concur that the examples below are correct with respect to using both one en-dash and hyphens within the same phrase?

    Examples:

    20–30-foot boards
    a 50–100-mile radius
    25–35-year-old men
    10–15, 25–35, and 40–45-milligram tablets

    $45 million–$55 million-a-year business
    (No hyphen after $45 and $55; correct?)

    $250,000–$300,000 per year business

    • We find your use of both an en dash and hyphens to be creative and acceptable to us. However, we are unable to find this sort of usage in any of our usual reference books such as the Chicago Manual of Style or the Associated Press Style Book. If you locate anything further on this topic, please send it along to us.

  13. Wendi says:

    What about fractions?

    I have a technical guide that has:
    Using (3) 2 1/2-in. screws per corner, construct a 4 ft. x 8 ft. frame.
    (12) 2-1/2 in. Wood Screws

    • As the post states, hyphens are never used between the numeral and the abbreviation. Also, the fraction 2 1/2 does not contain a hyphen, and we see no reason to capitalize “wood screws.” This method of writing “(3) 2 1/2” and “(12) 2 1/2” is efficient for saving space. Therefore, we recommend the following:
      Using (3) 2 1/2 in. screws per corner, construct a 4 ft. x 8 ft. frame.
      (12) 2 1/2 in. wood screws

      or, if space allows:
      Using three 2 1/2 in. screws per corner, construct a 4 ft. x 8 ft. frame.
      Twelve 2 1/2 in. wood screws

  14. Gurmeet says:

    Street No.-5 or Street No.5 which is correct way of writing ?

  15. Paulina Messina says:

    What about when using fractions? Would it be correct to say:

    7 1/2-inch molding

    1/2-inch to 5/8-inch thick

    Also, which could be correct: 400-Amp electrical service or 400 A electrical service?

  16. M says:

    I am having a discussion with a doctor. We submit lab samples and dictate how they are submitted. Is either example more correct than the other? See below:

    Sections are submitted labeled (A1-A2).
    Sections are submitted labeled (A1 & A2).

    • The major style manuals advise that the ampersand should not replace the word and, except in widely accepted abbreviations. See our post & What About the Ampersand? The parentheses are unnecessary here. Since it appears you have only two labels, write “Sections are submitted labeled A1 and A2.”
      If you would like to be more specific, you could write:
      “Two sections are submitted labeled A1 and A2.”
      “Five sections are submitted labeled A1-A5.”

  17. Deb Lamoureaux says:

    I am having an argument on units of measurement. (see below) which is correct? 60-inches or 60 inches?
    My assumption is when you are describing a specific measurement it is hyphenated but when you are describing how many inches it is not.
    Which is right?

    NPS 1/2: Maximum span, 60-inches; minimum rod, 1/4-inch. OR
    NPS 1/2: Maximum span, 60 inches; minimum rod, 1/4-inch

    • Following the guidance of The Chicago Manual of Style, measurements are only hyphenated when used as adjectives, and even then only according to how the units of measurement are expressed. For example:
      The pipe span is 60 inches.
      The pipe covers a 60-inch span.
      The pipe covers a 60 in. span.

  18. Diana Buchanan says:

    Please let me know if this is acceptable (if not correct):

    Wells are constructed of 2- or 4-inch-diameter, Schedule 40, polyvinyl chloride (PVC) casing with 0.010-inch, factory-slotted screen installed between 10 and 25 feet below ground surface (bgs).

    (There’s a lot there, I know.)

    I am a geologist who writes and reviews technical reports, and I work with people who tell me, “It just doesn’t look right,” so I very much appreciate being able to show them your posts. Thank you!

    • Your hyphens look fine to us; however, we would cut back on commas:
      Wells are constructed of 2- or 4-inch-diameter Schedule 40 polyvinyl chloride (PVC) casing with 0.010-inch factory-slotted screen installed between 10 and 25 feet below ground surface (bgs).

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