[Editor’s note: This post relies on the 16th edition of CMOS, which is no longer supported.]

7.85 Hyphens with Numbers + Nouns

How many times have you wavered over putting hyphens into an expression that combines numbers with some kind of measure?

Is the child six-years-old or six years old?
Is the trail six-miles-long or six miles long?

The Chicago Manual of Style 7.85—our famous hyphenation table—covers this topic in section 1 in the row called “number + noun.” The general guideline is that such phrases are normally left open but are hyphenated when they come before a noun and act as a unit to modify it.

Examples

The child is six years old.
The six-year-old child is theirs. (“Six-year-old” modifies child.)

That trail was six miles long.
He took the six-mile-long trail. (“Six-mile-long” modifies trail.)
or He took the six-mile trail.

The book has 432 pages.
I read a 432-page book. (“432-page” modifies book.)

The pumpkin weighed ten pounds seven ounces.
The prize went to a ten-pound-five-ounce pumpkin. (“Ten-pound-five-ounce” modifies pumpkin.)

The gate needs to be six and a half feet wide.
It will be a six-and-a-half-foot-wide gate. (“Six-and-a-half-foot-wide” modifies gate.)

Troubleshooting

♦ When the hyphens start to pile up, it’s better to rephrase:

Problem: It’s a three-year-six-month-fifteen-day deadline.
Solved: My deadline is three years, six months, and fifteen days from now.

♦ Mixing hyphens and en dashes is awkward. Either rephrase or use all hyphens:

Problem: She has a $4–$5-million contract.
Solved: Her contract is worth $4–$5 million.
Solved: She has a $4-to-$5-million contract.

Numbers and abbreviations

In Chicago style, numerals + abbreviations have no need of hyphens when they come before a noun they modify:

the 33 m distance
a 2 kg weight
a 3 ft. high wall

Please see our commenting policy.