UNITS OF TYPE SIZE

Setting font size in pixels is the best way to ensure that the type appears at the size you intended (because percentages and ems are more likely to vary if a user has changed the default size of text in their browser).

Pixels are relative to the resolution of the screen, so the same type size will look larger when a screen has a resolution of 800×600 than it would when it is 1280×800.

You can also use pt for point sizes instead of px for pixels, but you should only do this when creating style sheets for printer-friendly versions of pages.

The default size of text in a web browser is 16 pixels. Using percentages of this amount, you can create a scale where the default text size is 12 pixels, and headings are sized in relation to this.