ISO 6346

The owner code consists of three capital letters of the Latin alphabet to indicate the owner or principal operator of the container. Such code needs to be registered at the Bureau International des Containers in Paris to ensure uniqueness worldwide. An owner can apply for more than one code, as normally the first 2 letters are used as the owner code and the third is used to indicate pool (e.g. HLA, HLB, HLX are some Hapag-Lloyd codes to indicate whether container is standard, reefer...)

The equipment category identifier consists of one of the following capital letters of the Latin alphabet:

• U for all freight containers
• J for detachable freight container-related equipment
• Z for trailers and chassis

Presently, all official BIC container codes end in "U". However, the Association of American Railroads recognizes similar codes for their containers and trailers travelling by rail in North America, though these are not recognized by the BIC and lack check digits.

Under the ISO code, then, only U, J, and Z are in use. The refrigerated (reefer) container is identified by means of the size type code.

The serial number consists of 6 numeric digits, assigned by the owner or operator, uniquely identifying the container within that owner/operator's fleet.

The check digit consists of one numeric digit providing a means of validating the recording and transmission accuracy of the owner code and serial number.

To compute the check digit, the letters have to be converted to numbers. This is done in three steps:

An equivalent numerical value is assigned to each letter of the alphabet, beginning with 10 for the letter A (11 and multiples thereof are omitted):

The individual digits of the serial number keep their numeric value.

Each of the numbers calculated in step 1 is multiplied by 2^position, where position is the exponent to base 2. Position starts at 0, from left to right.

The following table shows the multiplication factors:

If the final difference is 10, then the check digit becomes 0. To ensure that this does not happen the standard recommends that serial numbers should not be used which produce a final difference of 10; however, there are containers in the market which do not follow this recommendation, so handling this case has to be included if a check digit calculator is programmed.

Notice that step (ii) to (v) is a calculation of the remainder found after division of (i) by 11. Most programming languages have a modulo operator for this. Attention should be paid to how it works in the language chosen; i. e. if it gives back the decimal rest or the integer rest in order to get proper results. 11 is used as divisor because a container number has 11 letters and digits in total. In step 1 the numbers 11, 22 and 33 are left out as they are multiples of the divisor.

In day-to-day business it happens that containers do appear which do not follow the ISO 6346 identification at all; however, they are fully CSC safety approved containers. Usually these are "shippers owned" containers (SOC), which means that they are not owned by the carrier but supplied by the cargo owners (shippers). They may have no registered owner code and no category identifier and have no check digit. It is advisable to follow ISO 6346 as the absence of a compliant identification code causes problems for both carriers and container terminals to correctly identify the equipment and properly deliver the cargo, because computer systems require ISO 6346-conforming naming and as such missing prefixes are invented. For example, YYYY at the carrier and XXXX at the terminal causes the equipment to mismatch. Moreover, since ISO 6346 identification has become a requirement in international Customs conventions (Customs Conventions on Containers and Istanbul Convention), many Customs Administrations have begun validating that containers are marked as per the standard.