This entry is a continuation of an article I wrote a few months ago.
I noticed that this article has had a lot of views and clicks over the last month. Today I came across another wonderful source that can probably give you a better estimate of your word-count. It's a beta-version of a very exciting website under dictionary.com, and it's called "Word Dynamo". At first it will ask you your English language level. Since the website was mainly done for native-speakers, let me give you the break-down that will help you assess your "grade" level:
Elementary school: Elementary and Pre-Intermediate Level
Middle School: solid Pre-Intermediate and Intermediate.
High School: Upper-Intermediate
College +: Advanced.
If you're not sure what your level is try elementary and work your way up. The quiz is easy and interactive. Once you're done it will offer you a sign-up form to receive more quizzes in the future. Incidentally, my count this time was over 50,000 which was exciting. However, I will sign up to do more tests for something more challenging.
How many words do you know?