Dimensional Weight

Dimensional weight refers to density, i.e., weight per cubic foot. The weight of a shipment per cubic foot is one of its most important transportation characteristics, directly involving such factors as the efficient loading of an aircraft and the economy of freight traffic movement. Some commodities, such as machinery, have a relatively high density. Others, like ladies hats, have a relatively low density. Hence, the Dimensional Weight Rule was developed as a practice applicable to low density shipments under which the transportation charges are based on a cubic dimensional weight rather than upon actual weight. Examples: One pound for each 194 cubic inches of the shipment in the case of most domestic air freight; one pound for each 266 cubic inches of cut flowers or nursery stock shipments; and one pound for each 194 cubic inches of most international shipments. Some carriers give discounts for shipments of high density goods.
(Air Cargo from A to Z, Air Transport Association of America)