Although the 20 foot shipping container is no longer a favorite length for international shipping, it remains one of the ISO standard sizes, and it still is the basic unit of measure.
The 20 ft equivalent unit (TEU) is the building block for expressing shipping capacity. The length in a TEU could vary to 24 or 35 feet and still be expressed as 1 TEU. Only the width at 8 feet remains consistent between the various sizes. The height may vary from a 4 foot 3 inch half height 20 ft container, to the 9 foot 6 inch “high cube” container. The 8 ½ foot height is most common.
The height and exact volume don’t matter to the measurement; it still equals one TEU. A container of 40 or 45 feet would both equal 2 TEU in this “imperial” measuring system.
Likewise, 2 TEU equals 1 FEU or 40 foot container. Again, the exact height and mass of the container doesn’t matter. The TEU and FEU are called imperial measurements because the U.S. Defense Department needed standardization for war purposes but there was too much variability to make it all one, so they used an approximation method to standardize.
Maximum gross mass of a 20 foot shipping container for dry cargo is 24,000 kg and for a 40 foot container, regardless of the height, is 30,480kg. The payload maximum is 21,600 kg for the 20 foot container and 26,500 for the 40 foot version.
For many years the 20 foot shipping container was the standard length used by Matson and other major shipping companies. Matson found this size ideal for the goods it carried between U.S. west coast ports and Hawaii, and they fit comfortably into the hold of the converted World War II C-3 cargo ships Matson used for many years.
The operations research Matson ordered to verify optimal size in 1957 concluded that the 20 foot container up to a size of 25 feet in length was, indeed, optimal for Matson’s purposes. Matson ordered the 20 foot shipping containers to be built and they were stacked six high in the cargo holds and on the top deck of Matson’s freighters.
The 20 ft was never popular with trucking companies. They were too short to fit maximally on truck beds.
Frequently it was impossible for trucks to load two 20 foot shipping containers together because of road weight limitations. The optimal load size for most single bed trucks is 24 to 27 feet in length.
In the 21st century the 48 and 53 foot containers are more popular for international ocean-going ships. Many 20 foot containers lie abandoned at ship yards across the world because they are too small to be used in many cases, despite the importance of the 20 ft as a unit of measure.
A new 20 foot container can still be purchased from many manufacturers for shipping, storage and construction uses. As of December, 2011, used 20' containers on the retail market start around $1,600 without modifications or transport included. Prices can go as high as $4,000-5,000 if the container is in excellent condition. But 20' containers can be obtained for less than retail prices if you can purchase them in port cities.