Sea container numbers are an integral part of the shipping industry. The structure of sea container numbers is clearly regulated. Container numbers are used to identify containers, track their movement, and ensure a smooth international logistics process. As millions of containers are used in shipping, it is essential to have a unique identification system that ensures order and efficiency. This uniqueness is achieved by using container numbers assigned to strict ISO standards.
How is the container number compiled?
Owner code
The first three letters of the container number denote the owner’s code. This code makes it easy to determine which entity the container belongs to. For example, the code “MAEU” indicates that the container belongs to Maersk. All these codes are registered with the International Container Office (BIC) to ensure their uniqueness and avoid repetitions.
Equipment category identifier
The fourth letter of the container number shows what kind of container it is:
- U – cargo containers used for cargo transportation.
- J is the equipment of removable cargo containers.
- Z – trailers or chassis.
The owner’s code, along with this identifier, forms the so-called alpha prefix, which helps to quickly understand the purpose of the container.
Serial number and check digit
The fifth part of the number is a six-digit serial number assigned by the owner of the container. This number is unique to each container and allows you to distinguish it from others.
The serial number is followed by a control digit, which is used to check the correctness of the number. This figure is especially important in automated logistics and warehousing systems.

Additional characters and ISO code
In addition to the container number, each container has additional markings, such as the ISO code. This code provides information about the size, type and purpose of the container. For example, the code “45G1” refers to a 45-foot-high cube container for general purpose cargo.
Marking the container also includes the maximum weight, the mass of the container and the net weight of the cargo. This data is vital to ensure the safe transportation and storage of cargo.

Why is the structure of sea container numbers important?
Properly compiled and standardized numbers ensure the smooth movement of containers both in ports and in logistics networks. They allow you to quickly identify the container, track its condition and avoid mistakes when handling the cargo.
With unique container numbers, shipping and logistics companies can efficiently manage millions of shipments, reduce costs, and ensure a smooth international trade process.
If you have more questions about container numbers or their use in logistics chains, please contact us. Our team will be happy to help!
Structure of sea container numbers: unique numbers for identification and tracking. Learn how container numbers are compiled.