Does Windows 8 Explorer have a FolderSize column (or restore the column-handler API)?

This isn't a direct answer to the question, but possibly makes it slightly easier:

http://www.windows7hacker.com/index.php/2012/05/windows-7-tip-quickly-find-the-folder-size-in-the-folder-tooltip-in-windows-explorer/

Be aware that it does take a while for large folders and gives estimates in some cases.

I added a reference to the syntech's answer, but he has ignored it. I propose the Folder Size freeware tool.

I like it better than what syntech has proposed, because this tool provides more accurate results, works faster and does not have such a cluttered interface. The latest version can list system and backup folders and reveal better disk usage report than Windows Explorer. While Windows Explorer reported 98GB used on my SSD this tool reported that actually 116 GB were used. Give it a try.

Well no; unfortunately Windows 8 Explorer neither has a folder-size column built-in, nor supports shell-extensions like Folder Size. Moreover, even shell-extensions like Space Dolphin’s Size (which shows a tree of the sizes of all sub-directories of a folder in a Properties dialog tab) don’t work, or rather remain not working as they were broken in Vista.

Unfortunately to see the sizes of subfolders, users will have to continue to use external, third-party tools like WinDirStat and SequoiaView which is just not the same thing because at the very least, they do not let you see the folder sizes right there in Explorer and sort them (technically, some do have a folder-list view which approximates Explorer, but that is still just a work-around and not the same as an actual shell-extension).