PLARAIL Thomas and Friends 75th Aniversary Clear Thomas Island of Sodor set pre-order

parcels are not shipped purely on weight . The couriers use volumetric weight . ie The cost of a shipment can be affected by the amount of space that it occupies on an aircraft, rather than the actual weight.
 How to Calculate [b]Volumetric Weight[/b]

1. Multiply the parcel's three dimensions (length x height x width)
   
2. If you are using centimetres then divide the result by 5000 (or 4000 for EU economy services). ...
   
3. The resulting figure represents the volumetric weight of your parcel.