Branislav Pavlovic

 Function for text width measure in pixels:

(function($) {
     $.fn.textWidth = function () {
     $body = $('body');
     $this =  $(this);
     $text = $this.text();
     if($text=='') $text = $this.val();
       var calc = '<div style="clear:both;display:block;visibility:hidden;"><span style="width;inherit;margin:0;font-family:'  + $this.css('font-family') + ';font-size:'  + $this.css('font-size') + ';font-weight:' + $this.css('font-weight') + '">' + $text + '</span></div>';
     $body.append(calc);
     var width = $('body').find('span:last').width();
      $body.find('span:last').parent().remove();
     return width;
    };
 })(jQuery);

Call of the function:

var $input = $(input_element_id);
var text_width =  $input.textWidth();
alert(text_width);