There are two major measurement units: Fahrenheit and Celsius. Us crazy American enthusiasts often use the Fahrenheit system, while the rest of the world uses primarily the Celsius (metric) system.

Which should we use? Should we just specify both? Or does it matter?


4 Answers 4


We're big kids now, talking about the big stuff. Time to dust off the Kelvin and arm ourselves with it.

Seriously though, in a scientific situation Kelvin is usually used, especially in situations like these where the temperatures we deal with are usually at the extremes.

(Also, just like the policy on AmE vs BrE, we need not expect everything to be in one format. It's good to try to follow a standard though.

  • 1
    $\begingroup$ I like this idea, really. $\endgroup$
    – Undo
    Sep 24, 2013 at 19:49
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    $\begingroup$ As a fan of Fahrenheit, I concur. Outside of the troposphere, only Kelvin has any relevance. (And even I don't recommend Rankine. ;) $\endgroup$ Sep 24, 2013 at 20:17
  • $\begingroup$ Duh, I don't know why I didn't think of Kelvin. $\endgroup$
    – called2voyage Mod
    Sep 24, 2013 at 20:23
  • $\begingroup$ To be pedantically correct, the term is kelvin (plural: kelvins) rather than initial caps Kelvin. Think of the unit in terms newtons, ohms, amperes, etc. Give William Thomson, 1st Baron Kelvin his due respect and lowercase his name when writing about units of temperature. Only a very, very small number of scientists have earned the metrological distinction of having their names lowercased. Lord Kelvin is one of them. $\endgroup$ Jan 26, 2020 at 16:57

I think sticking to SI units would seem best. If someone needs to add, for example, Fahrenheit temperatures then that could be done within a parenthesis along with the Kelvin or Celsius. But, since there is a standard, we should stick to it.


I suggest we use Celsius in general, but if we are quoting or borrowing numbers from a source we should maintain their unit of choice (providing Celsius in parentheses). Fahrenheit can always be provided in parentheses for convenience.


I tend to respond using the same terminology a questioners use when I answer their questions.

If the questioner asks in terms of degrees Fahrenheit (°F for short), my response is likely to use those units, but parenthetically might also use degrees Celsius (°C for short) or kelvins (K for short), or both. If the questioner asks in terms of degrees Celsius I might toss in a parenthetical kelvins -- but not degrees Fahrenheit. Finally, if the questioner asks in terms of kelvins (K for short, sans the degree symbol), those are the units I'll use in my answer.

As an aside, the correct term is kelvins rather than degrees Kelvin or Kelvins. The spelling should be lowercase (kelvin rather than Kelvin), and the degree symbol (°) is superfluous. That the units are in lowercase when spelled out but uppercase when abbreviated is an extreme honor. Only a very small number of scientists have been metrologically recognized to the extent that have lowercase units named after them. Lord Kelvin is one of those scientists. Respect his name and lowercase it.

In addition, the degrees prefix in degrees Fahrenheit or degrees Celsius indicates that those scales are not absolute. The kelvin scale is absolute; the use of the degrees symbol in conjunction with the temperature unit "kelvin" (K for short, sans the ° symbol) is not needed and has officially been deprecated.


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