ISO 6346

ISO 6346 is the international standard from the International Organization for Standardization that covers the coding, identification and marking of intermodal shipping containers. It sets up a visual identification system in which every container carries an owner code of three capital letters registered with the Bureau International des Containers in Paris, an equipment category letter (U, J or Z), a six digit serial number and a single check digit, followed by size, type and operational marks. The check digit is worked out by giving each letter a numeric value, weighting each character by a power of two according to its position, and taking the result modulo eleven, which lets software confirm that a container number was recorded or transmitted correctly. Carriers and container terminals rely on computer systems that expect names in this scheme, so containers outside it cause mismatches in identification and delivery.