Which one is better to say? Volt or Volts?

Question

This question might be quite premitive, But I really want to know what is the standard way of saying for example:

2 Volts or 2 Volt
1 Volts or 1 Volt (the Volt seems to be a better choice!)
0.5 Volts or 0.5 Volt?

Answer 1

(When I gave this answer, I had in mind that, with your "Which is better to say?" you were meaning when writing. Now I see in your comment to Tony that you indeed mean when talking. When talking, W5VO's answer, in my opinion, is correct. My answer is still useful if someone is interested to know how to write them.)

Regarding case, unless that word starts a sentence (which is not the usual case), it should be written in lowercase. See Tables 1 and 3 in this page from the National Institute of Standards and Technology (NIST). So, when referring to the units themselves (without any quantity implied), you should write "volt", "volts", "joule", "joules", "watt", "watts", "ohm", "ohms", etc. All in lowercase.

Regarding singular/plural, see point #5 in this other page (also from NIST) to see an example ("The speed of sound is about 344 m·s-1 (meters per second)") that shows that plurals should be used for unit names, when needed.

Regarding how to express values of quantities, point #14 says that you should always use Arabic numbers and unit symbols (not unit names!).

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#14 : Numerals & unit symbols
Values of quantities are expressed in acceptable units using Arabic numerals and symbols for units.

proper:
m = 5 kg
the current was 15 A

improper:
m = five kilograms
m = five kg
the current was 15 amperes (incorrect!!!)

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So, to answer your question, you should write "2 V", "1 V" and "0.5 V".

"2 volts" / "2 volt" / "2 Volts" / "2 Volt" would be incorrect.

Answer 2

What sounds right to me is the following:

When describing a property of a device (not a measurement), the singular "Volt" sounds proper.

• This is a twenty Volt power supply.

When giving a measurement or a measurable number, the plural form "Volts" sounds correct.

• Increase the power supply output by 13 Volts
• I measured the battery and it was at 1.5 Volts
• The capacitor is 1.0 Volts away from being fully charged. (read as "one point zero", not "one")

When following "one" or "a", singular "Volt" seems appropriate.

• I need one Volt of signal to reach full scale.
• The supply is outputting seven tenths of a Volt.

Answer 3

"The American National Institute of Standards and Technology has defined guidelines for using the SI units in its own publications and for other users of the SI. These guidelines give guidance on pluralizing unit names: the plural is formed by using normal English grammar rules, for example, "henries" is the plural of "henry". The units lux, hertz, and siemens are exceptions from this rule: they remain the same in singular and plural. Note that this rule only applies to the full names of units, not to their symbols."

from here, highlighting by me.

Answer 4

I think the abbreviation avoids the issue. [V] ( ha )

The SI unit of measure is [volt] but when used in specifications, units of measure show respect by using Capital letters when named after a person and in singular mode. But in sentence form plural is used so we say a 10 Volt rating for a 100 Farad capacitor on 1000 Henry inductor coming from 7 Tesla generator.

BTW non-personal names like "radians" would be lower case. Latin powers of ten are often done either way. Not sure which is technically correct. So we see MHz for mega and mHz for milli Hertz and kV for kiloVolts an KHz for KillaHurtz... ha ha.

I beleive one may use lower case if there is no ambiguity like km.

I tend to say Hertz and Volts, because it sounds better, but in specs I use [Hz] and [V] .

So in casual use, it does not matter as long as you are consistent. But I am sure there is a military spec someone could find or from the SI standard.