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I am a little bit confused about using units in English, sometimes I hear that people use singular units for plural things, sometimes they use plural ones. Which one is correct?

  • 3 meter(s) long?
  • during a 2 week(s) period?
  • 0.5 dollar(s)
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In Standard English, this crucially depends on whether the phrase is prenominal or not. Prenominally, the phrase will not show plural marking, while elsewhere it will have the normal plural marking, as appropriate.

Compare:

  • The bureau is 3 meters long.

  • This is a 3-meter-long bureau. (prenominal)

  • The period is 2 weeks.

  • This is a 2-week period. (prenominal)

  • The bill was 0.50 dollars.

  • This is a 0.50-dollar bill. (prenominal)

Note also that a hyphen is normally inserted to connect the words in the adjectival phrase when the phrase is prenominal.

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  • Are you sure you should use plural even refering to less-than-one numbers? Wouldn't it be 0.50 dollar?
    – andrerpena
    Apr 22, 2011 at 3:20
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    @Ciwee: Yes, I am sure. You should probably read this answer from another question.
    – Kosmonaut
    Apr 22, 2011 at 12:16
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    The only time this doesn't hold true is if the stated quantity is 1. Only 1, if it's 1.00001 then it's plural again. The dresser is 1 meter long. It will take 1 week to get there. The bill was 1 dollar and some change. The bill was 1.15 dollars. The bill was one dollar and 15 cents. The bill was 1 dollar and 1 cent. Even plural with 0. The bill was 0 dollars and 86 cents. I have 0 apples and 1 orange.
    – Phoenix
    Nov 24, 2011 at 9:09
  • Dollars is a confusing example because we don't usually say "0.5 dollars" or "0.5 dollar" at all. If we substitute units of length then it's clear that we do pluralize: "The shelf is 0.3 metres wide",
    – Max Williams
    Apr 5, 2020 at 9:57
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See the NIST check list for a good concise reference about units in general. For hyphenated compound adjectives, which are in the singular: 3-meter long, a 2-week period. For the plural of noninteger quantities, the rule is that everything other than 1 uses the plural: 0.5 dollars.

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Simply put, units are inherently plural. For instance, the SI unit for time is seconds, the SI unit for mass is kilograms, and so forth. Therefore, when recording measurements, I think that it is acceptable to write “0.2 kilograms” and “0.95 seconds.” An equivalent expression for this example is “two-tenths of a kilogram” and “ninty-five-hundredths of a second.”

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  • Your answer is good so far, but it doesn't address the second example. Why would one say "a two week period" instead of "a two weeks period"?
    – TaliesinMerlin
    Dec 26, 2018 at 3:40
  • All measurements come with a precision which indicated by the number of digits after the decimal point (even if these happen to be zero). Is it "1.0 kilograms" or "1.0 kilogram" then for an object of mass exactly equalling 1.0000001 kg?
    – Oskar Limka
    Sep 30, 2021 at 8:56
  • That's not actually correct. The SI unit for time is the second, for mass the kilogram. All singular. But the second point still stands: when using the names, you should use them as any other name in the language used (i.e. English in this case), including the plural form where needed (and other things such as capitalization rules). Unit symbols however are always singular.
    – Roel Schroeven
    Jun 2 at 15:21
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In this case, as in many cases with the English language, one shouldn't try to use too much logic. There are things which I wouldn't touch with a ten-foot pole, and what kind of pole is that? One with a length of ten feet.

IIUC, this language particularity goes back rather far in the history of the English language, as it also exists in Dutch.

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    – Jiminy Cricket.
    Apr 5, 2020 at 13:05
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It is common in informal spoken English, at least American, to omit the plural.

I got me a new fish pole, ten foot long!

Correct usage would be to say, "ten feet long."

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  • 4
    Correct usage would be to say "I bough a new fish pole..."
    – Brian Carlton
    May 30, 2012 at 18:39
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    @BrianCarlton bough, as in the noun bough?
    – Kent Munthe Caspersen
    Dec 28, 2015 at 17:58
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    I’m not going to touch this one with a ten foot pole!     :-)    ⁠
    – Scott - Слава Україні
    Jun 26, 2018 at 3:17
  • No; feet/foot is a special case. You wouldn't say "I've found a ruler eighteen inch long!" or "This wall is three metre high" or "The next lockdown could be two month long!" 'Foot' is better regarded as an invariant alternative plural.
    – Edwin Ashworth
    Oct 26, 2020 at 15:32

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