What is the relationship between ems and pixels?

Question

What is the value of an em in terms of pixels?

10em = ?px ?

Answer 1

There's no specific relationship between em and px. It's computed based on the width of the "m" character for each font-face.

Answer 2

While as others have said, there is no set ratio - as it varies from font to font - it is possible to calculate this for a particular font face/size combination by using DHTML.

Simply create a div with

style="width: 1em; visibility:hidden"

and append it to the place in the document you are interested about.

You can then find out its width by checking the div's clientWidth property

Answer 3

It depends on the font and the platform you're rendering on. There is no universal ratio.