From 1 July 2016, the IMO (International Maritime Organisation), as part of the UN, will require "verified" gross weights to be issued for all containers prior to shipment in order to ensure the safety of ships and people. This UN requirement will be implemented in national legislation in all countries worldwide.
The specification is:
"A packed container will not be loaded on board vessels unless the Verified Gross Mass (VGM) of the container has been provided to the Carrier and terminal, or their representatives, sufficiently in advance."
The VGM (Verified Gross Mass) is made up of the gross weight of the load with packaging, plus load securing material and the empty weight of the container (via the transport logistics company).
From you, as the client, we only need the information according to ADSp (2016), section 3.1.1 "... the gross weight (of the goods) including packaging and loading equipment. ..." [Section 3: "The principal is obliged to inform the freight forwarder in good time before placing the order of all significant circumstances affecting the execution of the order."]