You can easily do that by comparing scrollHeight with clientHeight, try the following:
<script type="text/javascript">
function GetContainerSize ()
{
var container = document.getElementById ("tempDiv");
var message = "The width of the contents with padding: " + container.scrollWidth + "px.\n";
message += "The height of the contents with padding: " + container.scrollHeight + "px.\n";
alert (message);
}
</script>
For more information please take a look at: http://help.dottoro.com/ljbixkkn.php