font sizes question

I know we have a lot of font groupies here. I like playing with fonts but have been wondering:

Why aren't sizes consistent across the different typefaces?

I mean, a size 12 takes up different space both vertically and horizontally, depending on if I choose Cambria, Arial, Baskerville, Book Antiqua, Helvetica, Lucida Sans - these are not fixed-width fonts, I know.

Is it like women's clothing? One brand's size 8 is not another brand's size 8?

I'm remembering back to the days of typewriters - pica vs elite. Those sizes didn't match up, either.

When I'm goofing around with my ms instead of actually writing I use different fonts to get my creative juices flowing, seeing what they look like on the page. One size 12 font can take up a lot more pages than another one does.

Why? Why no consistency?

Yeah, yeah, TNR or Courier (and *not* Courier New according to some people).

I guess I'd think they would be consistent in sizes for the same reason wrenches come in consistent sizes, the same way screws and nails are consistent ...

For printing, a font is not just a pretty symbol on a page, it's also a tool, in a way.

If you know how much space a size 12 takes up, no matter now many curlicues it has or doesn't have, then it's easier to know how much pieces of (consistently sized) paper you need.

Easier to know if my poor old eyes can read it easily. I like size 12 for reading, in general, but some size 12s are too small.

I'm just curious about a lot of things. I was probably one of those, "But why Mom?" kids.