Have you ever wondered how many English words you know? The question is not very precise — what does it mean to ‘know’ a word? is teacup a word or a combination of two words? how about tick off? is game (something you play) a different word from game (wild animals)? Nevertheless, it feels good to put some kind of number on your vocabulary.
Testyourvocab.com will estimate the size of your passive English vocabulary (the words that you can understand; not necessarily use in a sentence) by showing you a sample of words from a dictionary to determine your general level, and then another sample to get a more precise measurement. You can then compare your result with native speakers and non-native speakers of various ages.
The authors have also published some interesting charts based on the data they’ve collected.
P.S. In case you’re wondering, my score was 26,400.