[zeristor]

I don't know if this is that link, but it fits the bill:

http://testyourvocab.com/

It gave me 36,800

I'm encouraged that there are more words for me to learn

[p1esk]

To illuminate these numbers, the vocabularies of famous English writers range from 15,000 to 30,000 unique words [1].

[1] https://zwischenzugs.wordpress.com/2011/03/06/shakespeare_un...