Size of packet send between an IOS and a Read bear BLE shield +Arduino Mega2560

Hello .

I am trying to connect an Iphone 4s and a BLE redbear shield.Now They are connected to each other but I don't know how many byte in one packet send by 4s to BLE shield and vice versa...(I mean downloading and uploading)

by writing Serial.println(sizeof.....) couldn't show any thing in output. Would you let me know how can I measure the size of these packets?
I followed this site and procedure :
http://redbearlab.com/bleshield/

Regards