One of the nice features of the Cowriters.app is that it shows some nice statistics on your profile. Along the obvious streak length and post count there is also the total count of words written across all those posts.
Mine shows 129137 after yesterdays post. That's a lot of words. Quick googling gives 90000 words as an average word count of a book. So that's already almost halfway to a second book.
What's more astonishing is that coincidentally that post also happened to be my 600th post there. There used to be the 200 word daily minimum which I aimed to not go over too much. After the removal of the minimum I have written a few shorter ones. But in general I have tried to keep my posts around the 200 word mark.
Quick calculation based on these two numbers shows that, on average, I have been able to keep my post pretty close to that indeed. At a 215 and one fifth of a words per post I could afford to leave a couple of words per post out and still satisfy my goal.