Container number (ISO 6346)
MRN number
How does the ISO 6346 check digit work?
A container number consists of 4 letters (a 3-letter owner code + an equipment category letter: U for freight containers, J for detachable equipment, Z for trailers), a 6-digit serial number and a check digit. ISO 6346 maps each letter to a numeric value (A=10, B=12, C=13… — skipping multiples of 11), multiplies each of the first 10 characters by a weight of 2 to the power of its position, sums the results and divides by 11. The remainder is the check digit (a remainder of 10 is written as 0). This catches a single transcription mistake — say, from a booking into a declaration — before the wrong number reaches a port system.
How is an MRN structured?
An MRN (Movement Reference Number) always has 18 characters: two digits for the year the declaration was accepted, a two-letter country code of registration (e.g. PL, DE, NL), a 13-character declaration identifier and a check character at the end. The validator checks the structure — length, year, country code and character set. The check character algorithm is not published in EU legislation, so we do not verify it: a correct structure does not prove a declaration with this number exists in the customs system.
Frequently asked questions
What is the check digit in a container number?
It is the final, eleventh digit, calculated from the other ten characters per ISO 6346: each letter is mapped to a numeric value, each character is multiplied by a position-dependent weight, and the sum is divided by 11. A single typo or swapped digits will almost always fail validation.
What does "wrong check digit" mean?
Usually a typo: swapped digits, a digit misread from a document (e.g. 8 instead of 3), or a wrong owner code. Compare the number character by character with the bill of lading or booking. The validator shows which check digit would match the characters you entered.
Does the validator check whether the container exists?
No. The validation is mathematical - it confirms the number is correctly built per ISO 6346. We do not query the BIC register or carrier systems, so a valid number does not guarantee a container with that number is actually in circulation.
Do you verify the MRN check character?
No - for MRNs we validate the structure: 18 characters, declaration year, country code and the allowed character set. The MRN check character algorithm is not published in EU legislation, so we do not guess it. To confirm an MRN exists in the customs system, use the European Commission's MRN follow-up search.
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