Source: adapted from T. Toikka (2006) "The Real Price for Container Transportation between Asia and Europe", Lappeenranta University of Technology, Department of Industrial Engineering and Management.
Number of Units and Weight of Standard Consumption Goods that Can be Carried by a 20 Foot Container
Shippers try to use the volume and weight limits of the container in the most optimal way. Depending of the characteristics of the goods being carried, namely the weight-to-volume ratio, a 20 foot container may not be the optimal load unit. For instance, twice as much cell phones, DVD players or shoes could be carried on a 40 foot container without infringing the weight restrictions, which are around 27,000 kilograms. The cargo runs out of available volume before running out of available weight ("weighting out" versus "cubing out"). Since the costs of handling a 40 footer are not much higher than a 20 footer, there are notable advantages at using this load unit (or better a high cube 40 footer) instead.
For ponderous goods such as copying paper, the 20 footer is the optimum load unit as about 1,700 units each weighting just over 20,000 kilograms can be carried, which is the maximum permissible weight. Using a 40 footer for such a load, which is twice the volume, would carry only 2,150 units (27.6% more). Yet, a 20 footer may be a suitable unit for goods with a low weight-to-volume ratio if the demand of the consignee is not high enough to justify a more efficient load (40 foot) or if freight distribution is more dependent on higher frequency and smaller batches.