[Matre]

function getRealSize(element) {
	var clone = element.cloneNode(true);
	clone.style.position = "absolute";
	clone.style.top = "-1000px";
	clone.style.display = "";
	document.body.appendChild(clone);
	var sizes = {
		height: clone.offsetHeight,
		width: clone.offsetWidth
	};
	document.body.removeChild(clone);
	return sizes;
}

alert( getRealSize(document.getElementById('img_id')).width );