Hyphenation with Numbers and Units of Measure

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

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 16thedition 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.]

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