how i can calculate bandwidth usage for pppoe client via firewall

client address 1.1.1.254

i'm using this rule to calculate bandwidth usage
but it does not accurately calculate bandwidth usage

because when i'm trying to download 2Mb file the filter rule does'nt add file size to the bytes

i mean that when i download 2MB file size the filter rule bytes be some kilobytes only

i need only away to calculate bandwidth usage for one address using pppoe connection via firewall

i'm not good in english so i hope you understand me

thanks