jquery.textMetrics.js

// From here, with a few improvements (options classes argument, ability to pass plain text in):
// http://stackoverflow.com/questions/118241/calculate-text-width-with-javascript

(function($) {

  $.textMetrics = function(el, classes) {

    var h = 0, w = 0;

    var div = document.createElement('div');
    div = $(div);
    document.body.appendChild(div);
    div.css({
      position: 'absolute',
      left: -1000,
      top: -1000,
      display: 'none'
    });

    // 'el' might be html, or just plain text:
    div.html($(el).html() || el);
    // add any custom classes first:
    div.addClass($.makeArray(classes).join(' '));
    var styles = ['font-size','font-style', 'font-weight', 'font-family','line-height', 'text-transform', 'letter-spacing'];
    $(styles).each(function() {
      var s = this.toString();
      div.css({
        s: $(el).css(s)
      });
    });

    h = div.outerHeight();
    w = div.outerWidth();

    div.remove();

    var ret = {
      height: h,
      width: w
    };

    return ret;
  };

})(jQuery);