Size of User Chats

I need to see the size of all chats from users. I don't need see the content only the size. I don't agree in see what plp are talking since i consider it unethical this is why I just need the size. There is a feeling about the ejabberd server is decreasing Productivity of users, because they are chating alot when they should work. =/
So I would like to know if there is a way to see it. I saw something about save chats at ejabberd client, but I noticed its saved on each computer and need some configuration at client. I tryed the ejabberd log, but I didnt find a way to get it.

Tks for read.