In July 2012, I wrote a blog post on calculating the ideal font size for any viewing device. I’ve since written a JQuery plugin that typesets elements on a page automatically. I call it TypeSet. All settings are applied inline, for now, using relative em units. I still consider it a work in progress, it will probably have bugs, but I encourage you to check it out and give feedback!
The plug-in queries your monitor resolution and uses it to calculate what your ideal font size should be, and is designed to be future-friendly.
You might be wondering: What about mobile devices? Their screens are quite small, wouldn’t that shrink that calculated font size? In this case, TypeSet gets the users default font size, compares it to its calculation, and uses the larger of the two.