Total message size

Hello, is there a way to know the total size in bytes of the message (struct) sent? In case: header size (RSSI + ...) + body/payload size (sturct) + library encryption size (KeeLoq) + Ebyte encryption (CRYPT_H + CRYPT_L)? This is very important information to know if the LoRa transmission complies with local legislation. In some countries, the transmission cannot be longer than 400 milliseconds, and knowing the message size (head+body+encryption) is required.