Realize the size of your folders with TreeSize or FolderSize
TreeSize Free can be started from the context menu of a folder or drive and shows you the size of this folder, including its subfolders. You can expand this folder in Explorer-like style and you will see the size of every subfolder.
Scanning is done in a thread, so you can already see results while TreeSize Free is working. The space, which is wasted by the file system, can be displayed and the results can be printed in a report. There is a zipped version with no need to install and optional shell integration. You can delete undesired folders directly from inside TreeSize.
Another utility, called Folder Size, adds a “Size” column in Windows Explorer that displays the size of folders, while a new service at the background saves the size of folders for faster use next time you open a branch.