PixelToEm

http://github.com/davglass/yui-tools/blob/5ae0ed588feef376f10fa91dd5a2e9154cd12484/tools.js

/**
 * @method PixelToEm
 * @description Divide your desired pixel width by 13 to find em width. Multiply that value by 0.9759 for IE via *width.
 * @param {Integer} size The pixel size to convert to em.
 * @return Object of sizes (2) {msie: size, other: size }
 * @type Object
 */
        PixelToEm: function(size) {
            var data = {};
            var sSize = (size / 13);
            data.other = (Math.round(sSize * 100) / 100);
            data.msie = (Math.round((sSize * 0.9759) * 100) / 100);
            return data;
        },