H1-H6 font sizes in HTML

Question

In HTML (and in typography in general, I suppose), there appears to be some defined sizes for H1-H6 -elements.

Ie., if the baseline font size is 16px (or 100%), then h1

Answer 1

In a more general way, related sizes like this are often based on a geometric series, i.e. each successive number is bigger by a constant factor (something like 1.2, or sqrt(2)) from the previous one. There is the same kind of progression in the size of wrenches and hexagonal keys, or screw diameters, etc in mechanics, or in the A5/A4/A3… family of paper sizes.