I have about 700 books on my Kindle and another 500+ specialized physical books in related to my interests. I prefer to purchase for the Kindle whenever possible however there are still some reference type books that are not well suited as an ebook.
250-500. I used to have more, but I moved them all about 10 years ago and realized how dumb it is to hang onto a book I read and almost certainly will never read again; especially with Kindles and the like.
I have gradually winnowed down the number to a few hundred by taking them to a used bookstore and trading for new (used) books at about a 4:1 ratio. It’s gonna take a few more years to get to an amount that will fit on two bookshelves, which is my goal.
Mine’s a guess, but I’d say somewhere between 1,000 and 2,500. I have a lot of bookshelves, some of which have been relocated to the shed, the storage locker, and the garage. I really should go through and get rid of quite a few of them, at least the ones that don’t still have emotional significance.