Font sizes are RELATIVE TO EACH OTHER - WITHIN EACH DOCUMENT.|
So just make the font sizes whatever you want - for instance, titles are written in larger font sizes than the fonts in the rest of that same page. The title is the largest. The section titles are relatively smaller than the main title, but larger than the rest of the text. And footers are usually smaller yet.
The only situations where exact font size matters is when people are trying to print out a document - like for instance government forms that are available online for printing out, or scientific charts.
Be sure to click on the link above to Wasntme's comparison page that has font sizes, points, pixels and percentage sizes. This is the best comparison chart I've seen.
Individual users can set a minimum text size - and this will affect the APPARENT font sizes. The fonts will appear RELATIVELY smaller or larger than on someone else's computer screen.
If they set the smallest size large enough, then the font tag's smaller sizes will all look the same size. With a scan tag and the use of sizes specified in pixels, this can be overcome.
But the PROPORTIONS of small, medium and large size ranges will remain the same, relative to each other on the SAME page.
Ways To Write Text Size