In my lifetime? I can estimate, but it's probably not very accurate. I read about a book a week on average (that's just counting the ones I actually finish), and I read at least 2 a week when I was a teenager so...I dunno, thousands.
Yes, in your lifetime. I asked that question thinking that other people are doing like I'm doing, taking notes from the books I've read, and writing down the title and author. I'm doing this since I was in college, I like to remember the books I've read by reading the list.
I do keep a list of them (which is how I know I average about a book a week each year) but I haven't done that for my whole life, just a decade or so. I don't take notes on them, just the title and author, which I like to know in case I can't remember which books in a series I've read or who wrote a particular book.
I miss reading books...I haven't read one for pleasure in a while. I had to read ##Fault in Our Stars## for some work I was doing...I regret that that book was the last I picked up. I have read poems and short stories in the interim though.
How could anyone remember? 60 or so years. ago, I read lots to my daughters & now now grand-daughters. but I've never bothered counting them, as I'd never expected anyone to ask me that question! Since our daughters left home, I guess I have read 1 book a year.
I have been a prolific reader since childhood (70 years). I guess I would have read thousands of books in that time. Pretty catholic in my taste and will read anything (even cereal packets my husband used to say).
Although I will read any genre my preferred choice is crime fiction.