When it comes to font-size for a website, I personally would recommend using a global external stylesheet file and the following approach: the font-size forthe <body> is set to 62.5%, which resets it to 10px. Then, all font-sizes for particular page elements are set in em's, which has two benefits:
1) accessibility - since the font-size is set in relative units, the users can resize the text in IE6
2) predictability and ease for the developer - 1.1em = 11px, 1.2em = 12px, etc.
Please refer to the following page for more information:
the Telerik team