Web designers mostly use two font formats for body fonts that are pixels and em. I was always confused with em format of fonts but these days most of the web designers have started using em format. So if you are also confused with both the formats, here is an online tool to convert pixels to em.
PXtoEM.com is a online px to em converter which easily converts font format from pixles to EMs. Simply select your body font size and you will get conversions in em format based on your body font size in the next column.
Link: PXtoEm [via tothepc]