Assigned width in percentage but want to get it in pixels

One of options can be too, that parent element is not visible.
Here is example: http://jsfiddle.net/nDMM3/

You can see, that jQuery return width = 100 (like 100%)

.test {
    border: 1px solid;
    cursor: pointer;
    height: 10px;
    position: relative;
    width: 100%;
    display:none;
}

#test2{
   width:100%;
}

<div id="test1" class="test">
   <div id="test2">
      Hello
   </div>    
 </div>   

 alert($('#test2').width());