You could put styles you need to access with jQuery in either:

1. the head of the document directly
2. in an include, which server side script then puts in the head

Then it should be possible (though not necessarily easy) to write a js function to parse everything within the style tags in the document head and return the value you need.

You could access the document.styleSheets object:

<style type="text/css">
    .largeField {
        width: 65%;
    }
</style>
<script type="text/javascript">
    var rules = document.styleSheets[0].rules || document.styleSheets[0].cssRules;
    for (var i=0; i < rules.length; i++) {
        var rule = rules[i];
        if (rule.selectorText.toLowerCase() == ".largefield") {
            alert(rule.style.getPropertyValue("width"));
        }
    }
</script>

You can use the css(width) function to return the current width of the element.

ie.

var myWidth = $("#myElement").css("width");

See also: http://api.jquery.com/width/ http://api.jquery.com/css/

I have a similar issue in Getting values of global stylesheet in jQuery, eventually I came up with the same solution as above.

Just wanted to crosslink the two questions so others can benefit from later findings.

Most easy way

$('.largeField')[0].style.width

// >>> "65%"

A jQuery plugin based on Adams answer:

(function ($) {

    $.fn.getWidthInPercent = function () {
        var width = parseFloat($(this).css('width'))/parseFloat($(this).parent().css('width'));
        return Math.round(100*width)+'%';
    };

})(jQuery);

$('body').html($('.largeField').getWidthInPercent());​​​​​

Will return '65%'. Only returns rounded numbers to work better if you do like if (width=='65%'). If you would have used Adams answer directly, that hadn't worked (I got something like 64.93288590604027). :)

This is most definitely possible!

You must first hide() the parent element. This will prevent JavaScript from calculating pixels for the child element.

$('.parent').hide();
var width = $('.child').width();
$('.parent').show();
alert(width);

See my example.

Now... I wonder if I'm first to discover this hack:)

Update:

One-liner

element.clone().appendTo('body').wrap('<div style="display: none"></div>').css('width');

It will leave behind a hidden element before the </body> tag, which you may want to .remove().

See an example of one-liner.

I'm open to better ideas!

Building on timofey's excellent and surprising solution, here is a pure Javascript implementation:

function cssDimensions(element)
  var cn = element.cloneNode();
  var div = document.createElement('div');
  div.appendChild(cn);
  div.style.display = 'none';
  document.body.appendChild(div);
  var cs = window.getComputedStyle
    ? getComputedStyle(cn, null)
    : cn.currentStyle;
  var ret = { width: cs.width, height: cs.height };
  document.body.removeChild(div);
  return ret;
}

Hope it's helpful to someone.

Late, but for newer users, try this if the css style contains a percentage:

$element.prop('style')['width'];

There's nothing in jQuery, and nothing straightforward even in javascript. Taking timofey's answer and running with it, I created this function that works to get any properties you want:

// gets the style property as rendered via any means (style sheets, inline, etc) but does *not* compute values
// domNode - the node to get properties for 
// properties - Can be a single property to fetch or an array of properties to fetch
function getFinalStyle(domNode, properties) {
    if(!(properties instanceof Array)) properties = [properties]

    var parent = domNode.parentNode
    if(parent) {
        var originalDisplay = parent.style.display
        parent.style.display = 'none'
    }
    var computedStyles = getComputedStyle(domNode)

    var result = {}
    properties.forEach(function(prop) {
        result[prop] = computedStyles[prop]
    })

    if(parent) {
        parent.style.display = originalDisplay
    }

    return result
}

Convert from pixels to percentage using cross multiplication.

Formula Setup:

1.) (element_width_pixels/parent_width_pixels) = (element_width_percentage / 100)

2.) element_width_percentage = (100 * element_width_pixels) / parent_width_pixels

The actual code:

<script>

   var $width_percentage = (100 * $("#child").width()) / $("#parent").width();

</script>