Gridview Values

Question

Dear Friends,
I have a gridview in which there is packsize and rate per unit.
there is total field also the calculation of (packsize *rate per unit) =total

i have use rowdatabound() event but its not working.
when i enter the values in packsize and rate per unit. it should give me the calculated Total amount.

what could be done?

Pl reply,
regards,
aamir