Set width with function : width « jQuery « JavaScript Tutorial

<html>
  <head>
    <script type="text/javascript" src="js/jquery-1.3.2.js"></script>
    <script type="text/javascript">
        $(document).ready(function(){


            $("div").css("width",function() {
               return $(this).width() + 20 + "px";
            });
        });
    </script>
<style>

  div { margin:3px; width:50px; position:absolute;
        height:50px; left:10px; top:30px; 
        background-color:yellow; }
  div.red { background-color:red; }
  
</style>
  </head>
  <body>
    <body>
<div id="testSubject">

</div>
<div id="display"></div>
    </body>
</html>

30.115.width
	30.115.1.	Get width
	30.115.2.	Set width to
	30.115.3.	Set width with function
	30.115.4.	width(): find the width of div
	30.115.5.	width(val): If no explicit unit was specified (like "em" or "%") then "px" is concatenated to the value.