[Too]

Not in CSS, 1pt is always x pixels regardless of how many DPI you have.

[steveax]

Nope, it's way more complicated than that. Device pixels, CSS pixels, a pixel is not a pixel. PPK on the subject:

http://fronteers.nl/congres/2012/sessions/a-pixel-is-not-a-p...

Points are a terrible unit for specifying font sizes for the screen. Use px or proportional units (em, percentages, etc.). Points are for print, not screen.