How is an em calculated?

Question

I have noticed that you can use 1em and it will look different on different sites.

What is an em in proportion to?

• The font used?
• The bigges

Answer 1

The em is defined as the height of the capital letter "M" in the current font and size.

https://web.archive.org/web/20131127083352/http://www.guistuff.com/css/css_units.html