The container calculation unit, referred to as TEU, is the abbreviation of English Twenty Equivalent Unit, also known as the 20-foot conversion unit, which is the conversion unit for calculating the number of containers. Also known as the international standard box unit. It is usually used to indicate the capacity of a ship to load containers, and is also an important statistical and conversion unit for container and port throughput.

　　Most container shipments in countries use both 20-foot and 40-foot containers. In order to unify the calculation of the number of containers, a 20-foot container is used as a unit of calculation, and a 40-foot container is used as two calculation units to facilitate the unified calculation of container operations.

　　There is a term in the statistics of the number of containers: the natural box, also known as the "physical box." The natural box is a physical box that is not converted, that is, whether it is a 40-foot container, a 30-foot container, a 20-foot container or a 10-foot container is counted as one container.