How to Hyphenate Numbers Using the GPO

A writer with the National Oceanic and Atmospheric Administration recently stumped me with a question about numbers and hyphenation. He asked the following:

In our consultation documents (biops, letters,) we often see numbers connected to hyphens when describing a noun, but otherwise unhyphenated.  I try to remember this as something like: “The two 20-foot-long logs will be placed 20 feet apart.”

Is this right?

Also, what about areas?

And what about plural vs singular?

Examples:

  1. Removal of the existing bridge will remove approximately ### square feet of hardscape from the channel, and installation of the new bridge will place approximately ### square feet of new hardscape. (Correct?)
  2. The existing bridge is a ###-feet-long, ##-feet-wide, five-span structure constructed of concrete. (feet vs. foot?)
  3.  The action area includes approximately ### linear feet of _______ Creek (including ### feet of channel that will be dewatered and ### feet of channel downstream of the dewatered reach that may experience temporary alterations in flow and increases in turbidity), and the bed and banks of ______ Creek.  (Alternatively, ###-linear-feet, and ###-feet?)

hyphenThe question here is not how to present numbers but how to hyphenate them. So while it is tempting (and logical) to look in GPO Chapter 12, Numerals for an answer, a better place to search is Chapter 6, Compounding Rules, in particular 6.39 and 6.45, which deal with “Numerical compounds” and “Scientific and technical terms.”

The writer’s first question is when to hyphenate. The writer also asks how to manage plurals and singulars. Rule 6.39 reads as follows:

“A unit modifier following and reading back to the word or words modified takes a hyphen and is printed in the singular.”

“Unit modifier” means that the number and the measurement work together as an adjective to modify the noun, like “two 20-foot-long logs,” as opposed to “ten square-feet of hardscape,” where a prepositional phrase separates “of hardscape” from the number and measurement. So in order to be hyphenated, the words must appear directly in front of the noun without an intervening preposition.

Rule 6.39 also states that the unit modifier “is printed in the singular.” So the writer’s example #2 should read thus:

  1. The existing bridge is a ten-foot-long, five-foot-wide, five-span structure constructed of concrete.

For the moment, let’s set aside the question of what happens when the number and the unit of measurement are NOT acting as unit modifiers to address another rule, 6.45.

“Print a hyphen between the elements of technical or contrived compound units of measurement.”

This rule suggests to me that square-foot should be hyphenated as a technical unit of measurement. Other editors will probably interpret this differently based upon their own experience and preferences. The GPO does not specifically offer square-foot as an example, either here or in Chapter 7, Compounding Examples. So when applying this advice, you should use accepted common practice in your office or region. Still, I would edit the writer’s Example #1 as follows:

  1. Removal of the existing bridge will remove approximately ten square-feet of hardscape from the channel, and installation of the new bridge will place approximately ten square-feet of new hardscape.

You may be asking why the revision says “square-feet” rather than “square-foot.” Remember I said I would return to the unit modifier rule – here it is. According to 6.39, the measurement only changes to singular when it is acting as a unit modifier. In this case, “ten square-feet” is separated from the word “hardscape” by a preposition, meaning it is not working as a unit modifier. If it were, I would edit to read, “ten-square-foot hardscape.”

You should now be able to properly hyphenate any numbers and units of measurement in Example 3. The two questions you should ask are (1) do the number and unit of measurement work together as a unit modifier? and (2) are there any technical compound units of measurement?

  1. The action area includes approximately ### linear feet of _______ Creek (including ### feet of channel that will be dewatered and ### feet of channel downstream of the dewatered reach that may experience temporary alterations in flow and increases in turbidity), and the bed and banks of ______ Creek.  (Alternatively, ###-linear-feet, and ###-feet?)

NOTE: The answer will be posted Wednesday morning to my Facebook page. Good luck!

Comments

  1. Thanks for the guidance, it is helpful and cleared up a couple questions for me. But, although I know you said other editors may disagree, your choice to hyphenate “square-feet” was a surprise as I cannot recall a document ever representing it that way. I did some quick, expert, google searching (sarcasm included) and could not find a single example in that manner. Have you seen it often in documents where you are not the author?

    Thank you.

    • Tom, I struggled for a long time over the decision to hyphenate square-feet. You’re correct; I’ve never seen it hyphenated. But I don’t see how it differs from kilowatt-hour. Of course, compounds are often the subject of debate. Not so long ago to-day and to-night were hyphenated. So I’m owning the fact that this is the opinion of one, humble, editor.

      • So really what is being done is hyphenating a compound word unit to clarify that it is, actually, representing a single value, not a “square” and a “foot”, or a “kilowatt” and an “hour”; suggesting two separate unit measures. Is that what hyphenating is really representing?

  2. Requesting some clarification based on this guidance. I have just drafted this sentence and was wondering how to hyphenate “1,300 foot length”, if at all.

    This means in past consultations the ensonified area has never exceeded a 1,300 foot length, either upstream or downstream, from the noise source.

  3. Tom, yes, the two words are functioning together as a unit. And in your sentence, I would hyphenate foot-length, but not 1,300:

    This means in past consultations the ensonified area has never exceeded a 1,300 foot-length, either upstream or downstream, from the noise source.

  4. Matt Gaffney says:

    I think all the examples are correct as written. The only change I would make would be to substitute “###-foot-long” for “###-feet-long”; however, I don’t think there’s a hard-and-fast rule about using either foot/feet in such constructions. Local practice and convention guide such things. I was educated in parochial schools rather than public schools before 1965 and I suspect that my preference is based on the examples my teachers used and I further suspect that my teachers were influenced by their familiarity with the rules of Latin grammar.

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