In case anyone is still wondering this. Found this link today. http://www.nextofwindows.com/windows-7-tip-quickly-find-the-folder-size-in-the-folder-tooltip-in-windows-explorer
Windows 7 Tip: Quickly Find the Folder Size in the Folder Tooltip in Windows Explorer
Here is a quick tip that can be very useful and handy.
To quickly find out how big the size of a particularly folder is, simply hover over your cursor over to it in Windows Explorer.
A tooltip will popup which contains information of how big this folder is.
Yes, no more right click and properties. But here is a catch. The real calculation takes up to 3 seconds to calculate the total size under the selected folder. If the calculation hasn’t finished after 3 seconds, Explorer will just give up and reports the size
as “larger than X” where X was the size it managed to calculate within that 3 seconds.