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The plural form of physical units are always confusing me. I asked some senior students, some of them said we need to use plural form of units but some said units are always singular.

For example, 1 meter is 1 meter. But it is 3 times, should it be 3 meters? I know that if we use the abbreviation form, no plural form, i.e. 3m. But if we use 'meter', for the case like 0.04 meter, should it be 0.04 meter or 0.04 meters? I think we should use 0.04 meter because it is less than or equal to 1.

The last question I have is about foot and feet, when the magnitude is less than or equal to 1, I should use foot, otherwise, use feet instead, is that right?

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Nice and useful question but is it OK to say that this should have been posted on an English Grammar Stack Exchange, not physics? – Luboš Motl Aug 25 '13 at 18:04
And, @LubošMotl, it seems it was:, – Keep these mind Aug 25 '13 at 19:35
up vote 0 down vote accepted

"For example, the value 5 kPa is spelled out as “five kilopascals,” although “five kilopascal” is acceptable. If in such a single-unit case the number is less than one, the unit is always singular when spelled out; for example, 0.5 kPa is spelled out as “five-tenths kilopascal.”$^{[1]}$ But then it is always preferred to use all units in singular only for simplicity.

$[1]$: (See section 9.7)

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that's a good resource. Thanks. – user1285419 Aug 25 '13 at 16:46
By the way, NIST seems only about SI unit. Is that any handbook or resource (not online resource) have conversion tables on all SI and most non-SI but practical unit? Thanks. – user1285419 Aug 25 '13 at 16:49

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