I always thought that first variant (both letters written uppercase) is appropriate (maybe because I'm a Windows user), but recently I see more usages of second one (only first letter written uppercase). Which one is more eyes- and mind-friendly?

  • 1
    I think it will come down to personal preference - interesting reading here: english.stackexchange.com/questions/108213/…
    – Midas
    Mar 16, 2016 at 22:18
  • would you use all caps in all use cases if 'ok' is a part of a sentence?? I think it depends on your use case
    – Igorek
    Mar 17, 2016 at 1:16
  • Ok and ok are spelling errors. Check a dictionary for details. The correct spelling is OK or okay.
    – Mike
    Jan 22, 2020 at 20:22

6 Answers 6


Stick with is most common and time-proven. OK (with caps) has been used always. You can see its wikipedia page, is written using both caps.

  • 3
    Yes. This is not just a UI issue. The word is “okay” or “OK” not “Ok.” Mar 18, 2016 at 5:51

If you have space in your UI, maybe consider using a more indicative label like:

'Delete my stuff' 'Sign me up' 'Show me the report'

or the name of the page it takes you to.


OK is the more common one according to ngrams.

It's also worth thinking about how the appearance would affect someone reading aloud. OK is recognisable and forces a break between the letters ("oh kay"), while I've seen people slow down as they remember that Ok is the same thing and isn't "ok" or "och".

  • 1
    You forgot to check okay and Okay, too. Both are now more frequent than OK in that Google corpus.
    – Crissov
    Mar 17, 2016 at 15:17

There's also the pedantic answer to consider.

All dictionaries I am aware of list OK as the correct spelling for the word, never Ok. (In fact, the StackExchange spelling checker even flagged Ok as an error.) So Ok simply means you have a spelling error. One of the other comments mentioned practice in Denmark. I'm assuming we are discussing English, either US, UK, or some other major variant.

It is acceptable to use okay in written language, although Apple's documentation guidelines require the use of OK (search for "okay"). Most human interface guidelines that bother to point out the obvious say specifically to use OK in a button, though, not okay. See for example the Microsoft guidelines.

Finally, as a matter of clarity, a lot of sources now suggest not using an OK button at all, but replacing it with something more descriptive. See for example this article. It's not bed, despite the fact that the author didn't know how to correctly spell a key word in the title. :)


Whether you use OK or Ok could also be depending on the country/area - in Denmark, e.g. in informal texutual conversations the all-lowercase ok is seen a lot.

That being said, I would go for a button-label which reassures the user of the action which he is performing - as kelbyuk suggests.


Either 'Ok' or 'OK' should be fine, as long as whatever action about to be triggered by the button is crystal clear to the user.

That being said, to me, 'Ok' is cushy whereas 'OK' is serious, so I would use them accordingly based on characteristics of the product.

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