I'm working on a lighting product catalogue with products from many overseas suppliers. In regards to colour temperature, some of them put a space character before Kelvin symbol, some not:

4000K, 5600K


4000 K, 5600 K

Is there any official recommendation here?

Edit: It was suggested that this question is a duplicate of similar question related to computer symbols, suggesting it depends on style, and I happily agreed and considered that question as answered. However just now I've just found that there actually is an official recommendation related to SI unit symbols. Which makes the situation different than with units of computer storage.

  • This is arguably off topic but I wouldn't flag it as such (though we've had enough related questions that the SI handbook could become general reference).
    – Chris H
    Commented Aug 14, 2015 at 19:12
  • possible duplicate of Should thin spaces be used between numerals and units Commented Aug 14, 2015 at 19:35
  • Look at npl.co.uk/reference/measurement-units/si-base-units/the-kelvin The national physical laboratory is an authoritative source for this question.
    – Anton
    Commented Aug 14, 2015 at 23:43
  • 4000°K, 5600°K etc. Commented Aug 15, 2015 at 0:10
  • @EdwinAshworth It seems that for certain units, like official SI units, there are some official standards, but for other not. The linked question was in my opinion a more generic question, about any units, however it has one relevant answer. It seems that some units, like computer memory units, are OK with or without separating space.
    – ellockie
    Commented Aug 16, 2015 at 1:46

1 Answer 1


Official recommendation is to use space.

The value of a quantity is written as a number followed by a space (representing a multiplication sign) and a unit symbol; e.g., 2.21 kg, 7.3×10² m², 22 K. This rule explicitly includes the percent sign (%) and the symbol for degrees of temperature (°C). Exceptions are the symbols for plane angular degrees, minutes, and seconds (°, ′, and ″), which are placed immediately after the number with no intervening space.


  • You might like to improve your answer by citing your source with a link. The wording sounds like what I remember from the SI style guide, which for anyone working on these matters is worth reading and not (quite) as dull as it sounds. +1 from me though.
    – Chris H
    Commented Aug 14, 2015 at 19:10
  • To be more specific, this quote is from Wikipedia which refers to "the SI brochure" (from the International Bureau of Weights and Measures) and "the NIST brochure" (The National Institute of Standards and Technology), in the footnotes.
    – Henrik N
    Commented Aug 14, 2015 at 19:10
  • As it was my first answer, I was still trying figure out the formatting. Added the reference.
    – agni10
    Commented Aug 14, 2015 at 19:18

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