Slightly larger than most paperback books. However, the text was still too small for my wife to comfortably read without magnifying assistance.
So she reset the font size upwards and now reads her Kindle Fire comfortably without any additional magnification. The increased font size remains set on her Kindle for all books that she has; she doesn't need to reset it for each one. The only time that she has to play with it again is when Amazon pushes through a patch/update for the Kindle program and it resets to default. But she just sets it back to her level of font and goes on reading.
“Slightly larger than most paperback books. “
I had my eyes lasered some years ago and I went from near-sighted (great for reading) to instant old-man eyes where I need reading and computer glasses. I’m not going to make myself crazier trying to read mass-market paperback “pocket books” any more. It’s hardcovers and trade paperbacks for me now. Or an e-reader of similar size. :)