From the Kindle FAQ at Amazon forums:
Q: I know Kindle allows you to adjust [text] to an extent, but I from the illustrations I can't determine how it would really appear. Any information on this?
A: Kindle offers six different font sizes which correspond approximately to the following Microsoft Word standard font sizes:
1 = 7pt
2 = 9pt
3 = 11 pt
4 = 14 pt
5 = 17 pt
6 = 20 pt
So, if I am making a book from scratch thru Mobi-Creator, the "normal" typestyle in Word is 12 points. If I make the bodycopy of the text 12 points, does that hit at the [ 3 ] size above, leaving 2 smaller choices and 3 larger? (still making books to send to Dad, and just need to know how to predict what he will see).