How do I read a container number?

Three letters for the owner, one letter for the equipment type — U for a freight container — six digits of serial number, and a final check digit, often shown in a box.

How is a container check digit calculated?

Give each letter its ISO 6346 value (A = 10, skipping multiples of 11), multiply the ten characters by 1, 2, 4 up to 512, add them, and divide by 11. The remainder is the check digit; 10 becomes 0.

The owner part of a container number — three letters plus the category letter, such as MSKU — registered with the Bureau International des Containers in Paris.

Term

Container number (ISO 6346)

A container number is the 11-character identity painted on every shipping container under ISO 6346: a three-letter owner code registered with the BIC, a category letter (U for freight containers), a six-digit serial number and a check digit. The check digit catches typing errors — a wrong letter or digit usually fails the check.

Also called container number format, ISO 6346, BIC code, container check digitUpdated 13 October 2026

The four parts

Part	Example	What it is
Owner code	BIC	Three capital letters, unique and registered with the BIC
Category identifier	U	U for freight containers, J for detachable equipment, Z for trailers and chassis
Serial number	123456	Six Arabic numerals, with leading zeros if needed
Check digit	5	Calculated from the ten characters before it

ISO 6346, as the BIC describes it

Worked example: the check digit of BICU 123456

Letters take values from A = 10 upward, skipping 11, 22 and 33: B = 12, I = 19, C = 13, U = 32 · multiply each of the ten characters by 1, 2, 4 … 512 · 12 + 38 + 52 + 256 + 16 + 64 + 192 + 512 + 1,280 + 3,072 = 5,494 · 5,494 ÷ 11 leaves 5 → BICU 123456 5

The BIC's own sample number, and the check digit it publishes. A remainder of 10 is written as 0, which is why the GDV container handbook notes the standard's advice not to use serial numbers that produce it.

Who manages the codes

The Bureau International des Containers (BIC) registers owner codes; only codes registered with it may be used. The check digit depends on every character, including the owner code: the same serial number under a different prefix gives a different check digit.

The mistake people make

Typing a container number from a photo or a phone call without checking it. A transposed digit or an O for a 0 sends tracking queries, customs entries and delivery orders to a container that does not exist; running the check digit catches most of them before they leave the desk.

FAQ