jQuery - Get Width of Element when Not Visible (Display: None)

function realWidth(obj){
    var clone = obj.clone();
    clone.css("visibility","hidden");
    $('body').append(clone);
    var width = clone.outerWidth();
    clone.remove();
    return width;
}
realWidth($("#parent").find("table:first"));

Here is a trick I have used. It involves adding some CSS properties to make jQuery think the element is visible, but in fact it is still hidden.

var $table = $("#parent").children("table");
$table.css({ position: "absolute", visibility: "hidden", display: "block" });
var tableWidth = $table.outerWidth();
$table.css({ position: "", visibility: "", display: "" });

It is kind of a hack, but it seems to work fine for me.

UPDATE

I have since written a blog post that covers this topic. The method used above has the potential to be problematic since you are resetting the CSS properties to empty values. What if they had values previously? The updated solution uses the swap() method that was found in the jQuery source code.

Code from referenced blog post:

//Optional parameter includeMargin is used when calculating outer dimensions  
(function ($) {
$.fn.getHiddenDimensions = function (includeMargin) {
    var $item = this,
    props = { position: 'absolute', visibility: 'hidden', display: 'block' },
    dim = { width: 0, height: 0, innerWidth: 0, innerHeight: 0, outerWidth: 0, outerHeight: 0 },
    $hiddenParents = $item.parents().andSelf().not(':visible'),
    includeMargin = (includeMargin == null) ? false : includeMargin;

    var oldProps = [];
    $hiddenParents.each(function () {
        var old = {};

        for (var name in props) {
            old[name] = this.style[name];
            this.style[name] = props[name];
        }

        oldProps.push(old);
    });

    dim.width = $item.width();
    dim.outerWidth = $item.outerWidth(includeMargin);
    dim.innerWidth = $item.innerWidth();
    dim.height = $item.height();
    dim.innerHeight = $item.innerHeight();
    dim.outerHeight = $item.outerHeight(includeMargin);

    $hiddenParents.each(function (i) {
        var old = oldProps[i];
        for (var name in props) {
            this.style[name] = old[name];
        }
    });

    return dim;
}
}(jQuery));