The TEU was invented to size the container carriers. You can fit a mix of 20’ and 40’ containers in the middle butonly 20’ in some curved interior spaces. So the idea came to count how many imaginary empty 20’ containers one could place in a givencarrier, hence the Twenty foot-Equivalent Unit (in Mathematics, we might call this a lowest common denominator).
So then the TEU isa measure of the size of container carriers by counting the container slots. The TEU/Container slot is an inexact unit, and hencecannot be converted precisely into other units of measurement. The most common dimensions for a 20-foot (6.1 m) container are 20 feet(6.1 m) long, 8 feet (2.4 m) wide, and 8.5 feet (2.6 m) high, for a volume of 1,360 cubic feet (39 m3). But not all 20’ containers areequal: both 9.5 feet (2.9 m) tall High cube and 4.25 feet (1.30 m) half height containers are also reckoned as 1 TEU. This gives avolume range of 680 cubic feet (19 m3) to 1,520 cubic feet (43 m3) for one TEU.
Now you might have guessed it, an “FEU” is aForty-foot Equivalent Unit.
It was just created by analogy with the TEU but is very seldom used. Marketing might label a contract in FEU,i.e. the Freight will be perhaps a value in U.S. Dollars per FEU. If the shipper wants to use a 20’, then we divide the rate in half.