Wordchain network for English 3-letter wordsMy answer is a rather respectable 37,900, according to Test Your Vocab.com. In essentially two pages of checking words that you know from their list, the site determines your approximate vocabulary. The third page is just a few demographic questions for statistical purposes. That’s what they use to determine that the exact median score for adults is 27,123 words and that 37,867 is in the 95th percentile.