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)
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.
- 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.
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."
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.”