7 minute guide
ISO 6346 Container Number Check Digits
Understand owner codes, serial numbers and the check-digit calculation.
Container number structure
A standard freight container number has three owner-code letters, one equipment-category letter, six serial digits and one check digit. Spaces may be printed for readability but are not part of the number.
How the checksum works
Letters receive ISO values that skip multiples of 11. Each character is multiplied by a power of two, the sum is reduced modulo 11, and a remainder of 10 becomes check digit 0.
What a failure means
A failed check digit usually means one character was mistyped or misread. It does not prove the container itself is invalid, so compare the number with the door marking and source document.
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Extract the fields, then run deterministic shipping checks before export.
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