ISO 668 is the ISO standard number for shipping container dimensions.
The standard, formally titled “Series 1 freight containers—Classification, dimensions and ratings,” defines the principal external dimensions and ratings for widely used intermodal freight containers. Its standardization allows containers made by different manufacturers to fit ships, railcars, trucks, chassis and cranes across international supply chains.
ISO 668 covers familiar nominal lengths such as 20 and 40 feet, along with standardized widths, heights, corner positions and maximum gross masses. The dimensions are designed so containers can be stacked and secured using compatible corner castings and twistlocks. That compatibility is the engineering foundation of container interchangeability.
ISO 668 is often confused with ISO 6346, which governs container identification, including the owner code, serial number and check digit. Other ISO standards address testing, handling equipment and freight-container safety. Thus, ISO 668 concerns the container’s physical classification and dimensions, rather than its unique identity or operating procedures.