Quote Originally Posted by mklotz View Post
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The external volume of 1 TEU is 1,360 cubic feet, which is 38.51 cubic metres. The most common containers, used for transport on container ships and on lorries, are designated as 2 TEU.
And to make matters more interesting, there is often rounding used when describing containers. A 45ft container, which is 2.25 TEU is often just called a 2 TEU.

And ... a 20ft container is 1.5inches shorter so that a single forty can be stacked on two twenties and have three inches of space between the twenties.