What is height in em?
The meaning of "em" has changed over the years. Not all fonts have the letter "M" in them (for example, Chinese), but all fonts have a height. The term has therefore come to mean the height of the font – not the width of the letter "M."
Let's look at a simple example where we use the em unit to set font sizes:
<html>
<style>
h1 { font-size: 2em }
</style>
<body>
<h1>Movies</h1>
</body>
</html>
When used to specify font sizes, the em unit refers to the font size of the parent element. So, in the previous example, the font size of the
h1
element is set to be twice the font size of thebody
element. To find what the font size of theh1
element will be, we need to know the font size ofbody
. Because this isn't specified in the style sheet, the browser must find it from somewhere else – a good place to look is in the user's preferences. So, if the user sets the normal font size to 10 points, the size of theh1
element is 20 points. This makes document headlines stand out relative to the surrounding text. Therefore: Always use ems to set font sizes!
More Info
1em is equal to the current font size. 2em means 2 times the size of the current font. E.g., if an element is displayed with a font of 12 pt, then '2em' is 24 pt. The 'em' is a very useful unit in CSS, since it can adapt automatically to the font that the reader uses.
more here
1em is equal to the current font size.
2em means 2 times the size of the current font.
E.g., if an element is displayed with a font of 12 pt, then '2em' is 24 pt. The 'em' is a very useful unit in CSS, since it can adapt automatically to the font that the reader uses
Here's a link to other CSS units:
http://www.w3schools.com/cssref/css_units.asp