4. Counting from small to larger, left from right.
On my kindle 3(keyboard) that was the perfect size. On my Paperwhite the sizes don't quite match and I could use a 4.5 on caecelia condensed. 5 is just a bit big. I'd like a smaller step between the sizes.
But basically 4. That was the point of me being able to read again a lot because I had issues with the smaller print in paper backs. But then I am farsighted and need bifocals. So the closer something is, the blurrier it gets.
I don't think I would have ever been able to read on 1 much, even when I was a kid. At least not without a magnifying glass.
. I can do it for a few lines, until I squint my eyes out of my head that is.
Heck, I can't even read size 8 without my glasses. Not even with just the upper part of them. Need my reading bifocal part of them.
E-ink ereaders have given me the joy of reading back. Changing the sizing is a big part of that. Its pretty priceless for a lifelong reader.