How many English words to you actually know?

From the video “How Many Words Do You ACTUALLY Know?” comes this quiz VocabOwl: The Scientific Word Count, which claims to measure how large of a vocabulary you know. I took the quiz, which asks for the definitions of 100 words (twenty each from a basic list, intermediate list, advanced, export and grandmaster) and from that, estimates how many you know. I missed 6 out of the 100 words (two from the advanced category, and four from the grandmaster) and so, according to this quiz, my vocabulary consists of some 76,000 English words, for what it's worth.