Twenty-foot equivalent unit
The twenty-foot equivalent unit (abbreviated TEU or teu) is an inexact unit of cargo capacity, often used for container ships and container ports.  It is based on the volume of a 20-foot-long (6.1 m) intermodal container, a standard-sized metal box which can be easily transferred between different modes of transportation, such as ships, trains, and trucks. 
The container is defined by its length, although the height is not standardized and ranges between 4 feet 3 inches (1.30 m) and 9 feet 6 inches (2.90 m), with the most common height being 8 feet 6 inches (2.59 m).  It is common to designate a 45-foot (13.7 m) container as 2 TEU, rather than 2.25 TEU.
The standard intermodal container is designated as twenty feet long (6.1 m) and 8 feet (2.44 m) wide.  Additionally there is a standard container with the same width but a doubled length of forty feet called a 40-foot (12.2 m) container, which equals one forty-foot equivalent unit (often FEU or feu) in cargo transportation (considered to be two TEU, see below).
In order to allow stacking of these types a forty-foot intermodal container has an exact length of 40 feet (12.192 m), while the standard twenty-foot intermodal container is slightly shorter having an exact length of 19 feet 10.5 inches (6.058 m). The twistlocks on a ship are put at a distance so that two standard twenty-foot containers have a gap of three inches which allows a single forty-foot container to be put on top. 
The forty-foot containers have found wider acceptance, as they can be pulled by semi-trailer truck. 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 forty-foot container – in Europe and most other places a container of 45 feet (13.72 m) may be pulled as a trailer. Containers with a length of 48 feet (14.63 m) or 53 feet (16.15 m) 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.
|Length||Width||Height||Internal volume||TEU||Notes||Sq meters|
|20 ft (6.1 m)||8 ft (2.44 m)||8 ft 6 in (2.59 m)||1,172 cu ft (33.2 m3)||1 ||15,84|
|40 ft (12.2 m)||8 ft (2.44 m)||8 ft 6 in (2.59 m)||2,389 cu ft (67.6 m3)||2 ||29,77|
|48 ft (14.6 m)||8 ft (2.44 m)||8 ft 6 in (2.59 m)||3,264 cu ft (92.4 m3)||2.4||35,62|
|53 ft (16.2 m)||8 ft (2.44 m)||8 ft 6 in (2.59 m)||3,604 cu ft (102.1 m3)||2.65||39,53|
|20 ft (6.1 m)||8 ft (2.44 m)||9 ft 6 in (2.90 m)||1,520 cu ft (43 m3)||1 ||High cube||15,84|
|20 ft (6.1 m)||8 ft (2.44 m)||4 ft 3 in (1.30 m)||680 cu ft (19.3 m3)||1 ||Half-height||15,84|
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 cubic feet (2.83 m3).
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. The most common twenty-foot container occupies a space 20 feet (6.1 m) long, 8 feet (2.44 m) wide, and 8 feet 6 inches (2.59 m) high, with an allowance externally for the corner castings; the internal volume is 1,172 cubic feet (33.2 m3). However, both 9-foot-6-inch-tall (2.90 m) High cube and 4-foot-3-inch (1.30 m) half height containers are also reckoned as 1 TEU.  This gives a volume range of 680 to 1,520 cubic feet (19 to 43 m3) 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-foot (6.1 m) dry cargo container is 24,000 kilograms (53,000 lb).  Subtracting the tare mass of the container itself, the maximum amount of cargo per TEU is reduced to approximately 21,600 kilograms (47,600 lb). 
Similarly, the maximum gross mass for a 40-foot (12.2 m) dry cargo container (including the 9-foot-6-inch (2.90 m) High cube container) is 30,480 kilograms (67,200 lb).  After correcting for tare weight, this gives a cargo capacity of 26,500 kilograms (58,400 lb). 
Twenty-foot, "heavy tested" containers are available for heavy goods such as heavy machinery. These containers allow a maximum weight of 67,200 pounds (30,500 kg), an empty weight of 5,290 pounds (2,400 kg), and a net load of 61,910 pounds (28,080 kg).[ citation needed]
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