Em & Fonts

Definition of ems
An em is a unit of measurement in typography. This unit defines the proportion of the letter width and height with respect to the point size of the current font The unit was originally derived from the width of the capital "M" in a particular typeface. It is no longer defined in terms of any specific typeface, and therefore the same for all fonts at a given point size.

Some Popular Fonts http://www.ampsoft.net/webdesign-l/WindowsMacFonts.html
Arial
Arial Black
Comic Sans MS
Courier New
Georgia
Impact
Lucida Console
Lucida Sans Unicode
Palatino Linotype
Tahoma
Times New Roman
Trebuchet MS
Verdana
Symbol
Webdings
Wingdings
MS Sans Serif
MS Serif