It was a logical next step that shipping container sizes should be standardised. This was in order to be most efficiently stacked and so that ships, trains, trucks and cranes at the port could be specially fitted or built to a single size specification. This standardization would eventually apply across the global industry.
As early as 1960, international groups already recognising the potential of container shipping began discussing what the standard container sizes should be. In 1961, the International Organization for Standardisation (ISO) set standard sizes. The two most important, and most commonly used sizes even today, are the 20-foot and 40-foot lengths. The 20-foot container, referred to as a Twenty-foot Equivalent Unit (TEU) became the industry standard reference with cargo volume and vessel capacity now measured in TEUs. The 40-foot length container – literally 2 TEUs – became known as the Forty-foot Equivalent Unit (FEU) and is the most frequently used container today.