Unable to view folder size in list view

I'm simply trying to view folder sizes, and when looking at list view, with "Size" selected as a column (don't get me started on why you can't have separate columns for size & date modified...)  I only see dashes in the column;  when I check a folder and look at the "version history" sidebar, there is NO information other than a history of additions.  Nothing about size AT ALL.   This is so basic, I must be missing something... I can't imagine Dropbox would only let you view size of individual files?