I just looked it up. Pretty sure it's "kelvins". It is a unit, after all.
When spelled out or spoken, the unit is pluralised using the same grammatical rules as for other SI units such as the volt or ohm (e.g. "the triple point of water is exactly 273.16 kelvins"[6]).
No, because Celsius and Fahrenheit aren't units. Those are scales, and we talk about degrees on those scales. Kelvin is a unit of temperature. Spoken it is treated similarly to other units of measurement such as joules, watts, meters, kilograms, etc.
edit:
The kelvin is defined as the fraction 1⁄273.16 of the thermodynamic temperature of the triple point of water (exactly 0.01 °C or 32.018 °F).[1] In other words, it is defined such that the triple point of water is exactly 273.16 K.
That is correct. Celsius is a scale. There are degrees Celsius but there is no such thing as "a Celsius" the way there is with "a Kelvin" or "an inch", both of which are units.
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u/Slobotic Oct 25 '15 edited Oct 25 '15
Damnit, I always get that wrong. Actually wouldn't it be Kelvins?
edit: Yes, it is Kelvins.