Canadian · Validation
Shipping container number check digit validator.
Verify an 11-character ISO 6346 container number's real check digit, or enter just the 10-character body (owner code + category letter + serial) to have the correct check digit computed for you. Everything runs in your browser: nothing you type is transmitted anywhere.
Inputs
Result
Enter a container number and press Validate.
How the container number check digit works
An ISO 6346 container number is 11 characters: a 3-letter owner code, 1 equipment category letter (U for a freight container, J for detachable freight-container-related equipment, or Z for a trailer/chassis), a 6-digit serial number, and 1 numeric check digit.
To compute the check digit, each of the first 10 characters is converted to a numeric value: digits keep their own value, and letters map to a table that deliberately skips every multiple of 11 (A = 10, B = 12, C = 13 … skipping 11, 22, 33 … up to Z = 38). Each value is then multiplied by 2 raised to its position (position 0 for the leftmost character, so weights double at every step: 1, 2, 4, 8 … 512), and all 10 products are summed. Take that sum modulo 11: if the remainder is 10, the check digit is 0; otherwise the check digit is the remainder.
The published worked example, CSQU3054383, confirms this end to end: the first 10 characters "CSQU305438" produce a weighted sum of 6185, and 6185 mod 11 = 3, matching the real container number's final digit.
What a passing checksum does and doesn’t tell you
A valid check digit only proves the characters are internally consistent — it does not confirm the owner code was ever actually registered with the BIC, or that a real container carries this number. For that, look the owner code up in the BIC's public register. This tool runs entirely in your browser: nothing you type is transmitted, stored, or logged.