container number validator
How the container number format works
- Format
- 3-letter owner code + 1 equipment category letter (U/J/Z) + 6 digits + 1 check digit
- Example
- CSQU3054383
Things to watch for
- The 4th letter is the equipment category, not part of the owner code: U = freight container, J = detachable equipment, Z = trailer/chassis
- The check digit is computed by giving each of the first 10 characters a value (letters use a table that skips multiples of 11) multiplied by an increasing power of 2, then taking the sum mod 11 — a valid checksum confirms the format only, not that the container is registered with BIC
- Container numbers are usually printed with a space before the check digit (e.g. CSQU 305438-3); strip the spacing before entering it here
^[A-Z]{3}[UJZ][0-9]{7}$A container number is the 11-character code defined by ISO 6346 that identifies one specific intermodal shipping container as it moves between ships, trains, trucks, and terminals — the equivalent of a license plate for a box that might cross a dozen borders and change hands several times in a single journey. It’s built from a 3-letter owner code, a 4th letter marking the equipment category, a 6-digit serial number, and a trailing check digit, and it’s what lets carriers, ports, and customs systems all reference the exact same physical container across completely different computer systems.
How this validator works
This check confirms the string is 4 uppercase letters (with the 4th restricted to U, J, or Z) followed by 7 digits, then recomputes the final digit as a checksum over the first 10 characters. Each character gets a numeric value — digits use their face value, letters use a lookup table that skips multiples of 11 — multiplied by 2 raised to its position, summed, and reduced mod 11 (a result of 10 wraps to 0). That’s the same arithmetic terminal and EDI systems run automatically, so a mismatch here catches exactly the kind of misread letter or transposed digit that would otherwise get a container flagged or delayed at a gate.
What a pass doesn’t tell you
A pass confirms the number is structurally valid and its checksum is arithmetically correct — nothing about whether that specific container physically exists, is currently in service, or is registered to the owner code it starts with. That verification runs through the BIC’s own registry, not a public format checker.
Content last reviewed 2026-07-23.
container number FAQ
What do the four letters at the start of a container number mean?
The first three are the owner code, a unique 3-letter identifier for the leasing company or carrier that owns the box, registered with the BIC. The fourth letter is an equipment category, not part of the owner code: U means a standard freight container, J means detachable freight-container-related equipment, and Z means a trailer or chassis.
Why does the ISO 6346 check digit use a table that skips multiples of 11?
Each of the first 10 characters (letters and digits) is converted to a numeric value, multiplied by an increasing power of 2, and summed; the total mod 11 gives the check digit. The letter-value table deliberately skips every multiple of 11 (11, 22, 33...) so that no letter maps to a value that would break the mod-11 arithmetic — it's a design choice built into the standard, not an arbitrary gap.
Does a valid check digit mean the container is registered with BIC?
No. This tool only confirms the 11 characters are correctly formatted and that the check digit matches what the mod-11 formula predicts for the first 10 — that's arithmetic, not a lookup against BIC's owner-code registry. Confirming a specific box is actually registered and in service requires checking BIC's own records, not a format validator.