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());

.width() gets "...the current computed width" of the element that is used on, per the jQuery width documentation: http://api.jquery.com/width/, so the return value from $('#heatMapBar').width() is in pixels, not percent. I would suggest using developers tool to check the width, it may be that in #heatMapBar's current context, its width is 100px.

If you look here: http://jsfiddle.net/NkQXa/1/ you will see that #test is set to width:50%;, but it alerts the actual pixel width.

There can be a problem with multiple divs having percentage width:

<div style="width: 50%">
<div id="getMyWidth" style="width: 100%"></div>
</div>

In this case it returns 100 as width for the inner div for me. I solved it by taking the width of the outer div.

Another solution without jquery is to use the property clientWidth available on HTMLElements

document.getElementById('test1').clientWidth

Based on Honzik's answer there this is a small workaround in case the element needed to specify it's width is inside a hidden parent element.

function getWidth(elemID) {
    // get parent element unique id (must have)
    var parentId = $("#"+elemID).parent().prop("id"); 
    // remove the child element based on the specified element id
    $("#"+elemID).remove();
    // append a new child element but on body where most probably is not set to "display:none"
    $("body").append('<div id="'+elemID+'">Hello</div>');
    // get the width of the newly appended child element and store it to a variable
    var width = $("#test2").width();
    // remove child element from body
    $("#"+elemID).remove();
    // re-append child element to its former position under former parent element (having CSS attribute "display:none")
    $(parentId).append('<div id="'+elemID+'">Hello</div>');
    // display stored element width 
    alert(width);
}
// usage to get the element's width
getWidth("test2");

Try it in the below snippet!

function getWidth(elemID) {
        var parentId = $("#"+elemID).parent().prop("id"); // your parent element should have a unique id specified
        $("#"+elemID).remove();
        $("body").append('<div id="'+elemID+'">Hello</div>');
        var width = $("#test2").width();
        $("#"+elemID).remove();
        $(parentId).append('<div id="'+elemID+'">Hello</div>');
        alert(width);
    }
getWidth("test2");

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

#test2{
   width:100%;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="test1" class="test">
   <div id="test2">
      Hello
   </div>    
 </div>