About 600 books - I only keep them if I have a reason to, for example if I think I’ll re-read or reference them, or they have huge sentimental value like some books from my childhood. I used to have about four times that many, but I realised I had no reason to hang onto them and they were taking up a lot of room in my home. Speculative fiction (sci-fi/fantasy) is about half of that, with other fiction and non-fiction making up the rest.