Container number check (ISO 6346)

Every shipping container carries an eleven-character identity under ISO 6346: four letters and seven digits. The final digit is not arbitrary. It is a check digit, calculated from the preceding ten characters through a modulo-11 algorithm with positional weighting. Enter a container number and this tool will tell you whether that check digit is consistent — valid or invalid.

Container number check

A working tool — and a small illustration of what compliance really means.

Why this matters for an Authorised Economic Operator

A single invalid check digit is usually just a typing error. But a pattern of them, running through a cargo administration, is something an auditor reads differently. It signals that container numbers are being entered without verification — and a registration that isn't verified at the point of entry is a registration that cannot be fully trusted downstream. In OEA terms, this touches directly on process security and the integrity of transport-unit records — the domains a customs authority examines most closely. If the recorded identity of a unit cannot be relied upon, neither can the traceability that depends on it.

That is the difference between knowing that a check exists and understanding what its absence reveals. A container that arrives with a number that does not validate, or a seal number that does not match the one recorded at departure, is not a clerical curiosity — it is a question that a well-run operation should already have answered before the authority asks it.