There are many utilities out there that will show you the space used in the various folders on your system. One of the better ones is WinDirStat.
WinDirStat is a disk usage statistics viewer and cleanup tool for Microsoft Windows (all current variants).
WinDirStat reads the whole directory tree once and then presents it in three useful views:
* The directory list, which resembles the tree view of the Windows Explorer but is sorted by file/subtree size,
* The treemap, which shows the whole contents of the directory tree straight away,
* The extension list, which serves as a legend and shows statistics about the file types.