The researchers at TestYourVocab.com are gathering data on how many words people know. Take a short test, and the site will tell you approximately how many words you know.
According to the researchers' blog, average 30-year-old native speaker of English knows approximately 27,808 words. The Korean's vocab size was estimated to be 30,400. Not too shabby for a guy who picked up most of these vocabs by rote memorization, right?