em css question

[hargi]

What is em and why would you use it instead of px? looked at a few googled sites but can some one put it in laymens terms

 

[Ripper]

em means the text size isn't fixed. Basically the user can change the text size when viewing the site (CTRL+mouse scroll or View-Text Size), making it more HCI-friendly.

 

[Tripnologist]

Further to the above, I find the easiest way to use it is to set the body font size at 62.5% which will make 1em = 10px on most browsers (provided the user has left the font on default). This now makes it really easy to figure out proper sizes.