CSS Font Size Specifics

Question

I have a couple of specific questions about font size:

1. Is pt (I.E. 12pt) standardized? I think I read somewhere that pt = 1/72 of an inch. However, the size

Answer 1

1. In CSS 2.1 (the current spec), pt is unambiguously 1/72 of an inch. The reality is different, though, and this is reflected in the CSS3 Values and Units draft, section 5. It describes two setups, using different “anchor units”. If the pixel is the anchor unit, an inch (in as CSS unit) need not be an inch (the physical unit, 2.54 mm), and hence the meaning of p may vary as well. This is one reason why pt in CSS need not match pt in some software.

2. The font size is a basic property of a font. Any relationships between it and dimensions of characters are up to the font designer, but font design is of course not arbitrary. The CSS 2.1 spec puts this rather vaguely, but the formulation is still useful (against many common misconceptions): “The font size corresponds to the em square, a concept used in typography. Note that certain glyphs may bleed outside their em squares.” (And on the other hand, most glyphs use just a small part of the em square.)