Twenty-foot equivalent unit

The twenty-foot equivalent unit (abbreviated TEU or teu) is a general unit of cargo capacity, often used for container ships and container ports. It is based on the volume of a 20 ft intermodal container, a standard-sized metal box that can be easily transferred between different modes of transportation, such as ships, trains, and trucks.

Forty-foot equivalent unit
The standard intermodal container is 19 ft long and 8 ft wide. The height of such containers is most commonly 8 ft but ranges from 4 ft to 9 ft.

Another standard container is slightly more than twice as long: 40 ft, dubbed a forty-foot equivalent unit (often FEU or feu).

The reason the smaller container is 1.5 inches short of 20 feet is to allow it to be stacked efficiently with 40-foot containers. The twistlocks on a ship are set so that two standard 20-foot containers have a gap of three inches, allowing a single 40-foot container to fit precisely on top.

The 40-foot containers have found wider acceptance, as they can be pulled by semi-trailer trucks. The length of such a combination is within the limits of national road regulations in many countries, requiring no special permission. As some road regulations allow longer trucks, there are also variations of the standard 40-foot container; in Europe and most other places a container of 45 ft may be pulled as a trailer. Containers with a length of 48 ft or 53 ft are restricted to road and rail transport in North America. Although longer than 40 feet, these variants are put in the same class of forty-foot equivalent units.

Equivalence
The carrying capacity of a ship is usually measured by mass (the deadweight tonnage) or by volume (the net register tonnage). Deadweight tonnage is generally measured now in metric tons (tonnes). Register tons are measured in cu. ft, with one register ton equivalent to 100 cuft.

As the TEU is an inexact unit, it cannot be converted precisely into other units. The related unit forty-foot equivalent unit, however, is defined as two TEU.

It is common to designate a 45 ft container as 2 TEU, rather than 2.25 TEU.

The most common twenty-foot container occupies a space 20 ft long, 8 ft wide, and 8 ft high, with an allowance externally for the corner castings; the internal volume is 1172 cuft. However, both 9 ft High cube and 4 ft half height containers are also reckoned as 1 TEU. This gives a volume range of 680 to 1520 cuft for one TEU.

While the TEU is not itself a measure of mass, some conclusions can be drawn about the maximum mass that a TEU can represent. The maximum gross mass for a 20 ft dry cargo container is 24000 kg. Subtracting the tare mass of the container itself, the maximum amount of cargo per TEU is reduced to about 21600 kg.

Similarly, the maximum gross mass for a 40 ft dry cargo container (including the 9 ft High cube container) is 30480 kg. After correcting for tare weight, this gives a cargo capacity of 26500 kg.

Twenty-foot "heavy tested" containers are available for heavy goods such as heavy machinery. These containers allow a maximum weight of 67200 lb, an empty weight of 5290 lb, and a net load of 61910 lb.