The bigger of two numbers
Airlines charge on whichever is greater, the actual gross weight or the volumetric weight. Volumetric is the shipment volume in cubic centimetres divided by 6,000, which works out at 167kg per cubic metre.
A single pallet at 120 by 100 by 160 centimetres is 1.92 cubic metres, so it prices at 320kg however light it is. Two of those with 180kg of product on them are billed as 640kg. That is the whole trick, and it is the reason an air quote and an air invoice sometimes look like they belong to different shipments.
Where the money goes
Packing decides it. A carton with 30 per cent air in it pays for that air the whole way. Reducing a pallet height by 15 centimetres can take a full rate band off a shipment, and nobody at the airline is going to suggest it.
Height is usually the easiest dimension to attack, because pallets are built to a habit rather than to a measurement. The second easiest is a shipment split across two pallets that would fit on one.
What we do
We work both numbers off your packing list before you book, show you the two, and say which one you are paying. If the volumetric figure is the one being charged, we will tell you what the shipment would cost repacked, so you can decide whether the warehouse time is worth it.
That number is on the quote. It is not a service, it is arithmetic, and you should be suspicious of any air quote that does not show it.