Pixem allows you to copy and paste your stylesheet to convert all pixel values to ems and vice versa. A new stylesheet with the desired units will be generated on the right.
Want to convert a couple of individual values? Input a number followed by 'px' or 'em' into the input box on the left, and a conversion of that value will be on the right.
In order for you to take full advantage of this unique tool, I highly suggest watching the demo. Don't worry, It shows you exactly how to do it.
If you found a bug, or have any other questions or concerns, feel free to email me or tweet me. I look forward to hearing from you. Also, don't forget to share!