A nice tool that claims to access your English command (or, at least a rough estimate number of words that you may know):
1,500–3,000 words: a couple of years of English courses
4,000–7,000 words: intermediate English (4–6 years)
8,000–10,000 words: advanced English (8 years) for a particularly good student
Anything much beyond 10,000 words generally only comes from living abroad in an English-speaking country for a significant period of time, or else spending tremendous amounts of one’s own time exposed to English media (books, sitcoms, movies, etc.).