I find Microsoft Word's spell and grammar checker leaves a lot to be desired.
So I signed up with Grammarly a year ago and use it for checking grammar and spelling. It's handy and easy to use, there's a free and a premium version. I've been happy with it. Exceptionally useful.
The below image is a screenshot of the stats summarising my last twelve months. It appears I've checked* 842,279 words. In a year.
How much is 842,279? There's a big list at http://commonplacebook.com/. Consider:
All seven Harry Potter books: 1,084,625
Lord of the Rings: 455,125
Oliver Twist: 155,960
20000 Leagues Under the Sea: 138,138
Nineteen Eighty-Four: 88,942
Charlie and the Chocolate Factory: 30,644
* Checking is different to writing. In other words, I may have checked the same content twice. Or there was a technical fail.