Re: font sizes in ems

>An em is the term used to designate the square of any type size.
>Therefore an em will always be equal to 100% of any given type size in
>both the vertical and horizontal dimensions. Em is normally used in

This is how I understand it--from the Chicago Manual I have had for years.

>horizontal measurements such as margins and indents. In fact, until ems
>became a 'standard' CSS1 measure, I don't think I ever saw ems used to

Specifying margins and indents is why I think it's important of browser
vendors to implement them. Unfortunately, too many people only know "word
processor" typography. They want their familiar points and inches.

>handwritten markup that had to be understood by a typesetter. An em for
>12pt type is 12pt, regardless of font-family. 

I don't understand what is complicated about this idea. One em is the
point-size of the type. Possibly, they confuse em with one point.

>when they don't know the font-size of the text. Another situation where
>em is valuable is for indents and margins. Percent does not mean the
>same thing as em. A designer will typically specify indents in ems,
>because the most important relationship is to font-size, not to the
>horizontal dimension of the canvas.

Generally, I've tried to use percent for my margins because I want them to
be scalable. But I've know all along I wanted to specify them in em values.
If you watch percent margins, you'll see they change size with the browser
window, crushing the text. If you use a fixed margin value, they get very
narrow in relationship to the text. Yours is precisely the reason I want
ems, to specify margins so they relate to the *font size* (and hopeful they
might stay in good relation to the line length) not the window (or canvas).

David, you've helped clarify the terminology as it relates to CSS for me.
Thanks to you and others here. This talk of ems and the example pages
inspired me to add to a small test page of percent values. I had not
thought of combining percent and em on one page to compare them. The result
is at http://home.att.net/~knoblock/css/EM_TypeSheet.html with links to the
other pages. I've added David's and Hakons's definitions of an Em. I would
appreciate any suggestions or corrections.

Next, on to em margins.


   _/ Steve Knoblock                               editor@city-gallery.com
   _/ City Gallery                            http://www.city-gallery.com/
   _/ Member NSA               http://www.3d-web.com/nsa/nsa.htm