Are units in English singular or plural?

Question

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)

Answer 1

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.

Answer 2

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.

Answer 3

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."