Pressing (Win + E) keys launches Windows Explorer for easy browsing of contents including drives, folders and files. While files have size listing under size column (in detailed view), there is no size display for folders while viewing in Windows Explorer. Free utility ‘Folder Size’ can add this functionality and allow Windows Explorer show size for folders (just like size listing for files).
As seen in above screenshot, size column show respective sizes of both folders and files viewed under Windows Explorer. This utility only works with Windows XP and Vista. Unfortunately, Windows 7 users have to wait for compatible version or look some other utility with similar functionality. Download Folder Size for display of folders size in Windows Explorer.