How to Calcuate the Size of Message going thru PI

Hi ,

Does any one know how to calcuate how much Data has gone thru PI between a given Date range. Or how can I measure the size of a message which has gone thru PI .

This is in light of the fact that PI licance is based on the amount of message passing thru and my Customer wants to know if there is a standard report from where it can monitor the amount of messages which has gone thru.

Thanks & Regards

Gagan Kasana