disk usage discrepency

[songdove]

I look after a paid domain, and a free domain both hosted by W4C.

For some reason, the free domain's disk usage is somehow not entirely accurate.  I just got notification that the site was using 94% of its disk space.  I log into cpanel, I go to the disk usage area, and I pull out my calculator, and from the space usage listed in the directories there, I only come up with just over 13 megs used.  But when I look at my account information, it claims I have used just over 19 megs.  Which set of numbers is correct, and why would such a discrepency exist?  Are there areas of my hosting account that do not get reported in cpanel?

The paid hosting account doesn't seem to have this problem, at least not that I've noticed.   I need to know which set of numbers is accurate so I can go to the person I maintain the site for to let them know if they need to upgrade to the Starter account or not.