I think it should also be mentioned which font you are using, not just size. For example bitmap fonts look much bigger than scalable fonts generally even when they're set to same size. Scalable fonts also have some blurriness on them which make them look even smaller and need bigger sizes to be as readable as bitmap fonts.

I'm using bitmap fonts myself, XEN/11 for system default text and XHelvetica/13 for screen text (and Titanium/12 for desktop icons and NewRecall/13 for window icons). Mostly on 1920x1080/24" screen. Then I also have some 24 pixels high icon fonts on my 1680x1050/17" PB.. I put them on demonstration purposes, but they're still left there, I kinda like the big clear look if using scalable fonts :)

If I pick almost any scalable font sized 13, it looks (and is in practise) much smaller than my XHelvetica/13. And there seems to be differences between scalable fonts themselves too. I think a good measurement could be to compare actual sizes of upper case characters. For XHelvetica/13 upper case characters are 8 pixels high, for Bitstream Vera Sans/13 they are 7 pixels high, for Computer Modern/13, Open Sans/13 and Noto Sans/13 etc they're just 6 pixels and VERY blurry, they look almost like half smaller in real life! And that Geit's DejaVu Sans/13 gets only 5 pixels high upper case letters :p

You don't get the same real life experience by just looking the size value when selecting the fonts...


[ Edited by jPV 30.09.2016 - 15:55 ]