I think you're talking about the bars in your profile, right? Well, that's pretty subjective. It is based on your own judgement of your proficiency in a language. For example, in my case, I speak french much better than korean, but I do not think I'm just a beginner in korean, so I decided to choose the level 3.
To assess your level more accurately you would need to take an exam for that particular language, and then compare it to a standard, like the CEF or something like that.