How it is calculated
A container number has four parts: a three-letter owner code, a category letter (U for freight containers, J for detachable container equipment, Z for trailers and chassis), a six-digit serial number, and a check digit.
To work out the check digit, each letter is given a value (A = 10, B = 12, C = 13 and so on, skipping 11, 22 and 33), each of the first ten characters is multiplied by 2 to the power of its position (1, 2, 4, 8 … 512), and the total is divided by 11. The remainder is the check digit; a remainder of 10 counts as 0.
A correct check digit shows the number was written down correctly. It does not show that the owner code is registered with BIC, or that the container exists.
Sources
- Identification number, BIC (Bureau International des Containers)
- ISO 6346: check digit calculation, Wikipedia
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