If you have ever received a bill of lading or a shipping confirmation for sea freight, you have seen a sequence like MSKU1234567 or TCKU8872341. This is your container number — a unique identifier stamped on every shipping container in the world, governed by the ISO 6346 standard.
What Does a Container Number Look Like?
An ISO 6346 container number has exactly 11 characters: 4 letters followed by 7 digits. For example: MSKU 123456 7. Breaking it down — the first 3 letters are the owner code, the 4th letter is the equipment category identifier (almost always "U" for freight containers), the next 6 digits are the serial number, and the final digit is the check digit.
The Owner Code (First 3 Letters)
The owner code identifies the company that owns or leases the container. These codes are registered with the Bureau International des Containers (BIC). Common owner codes include MSKU (Maersk), TCKU (Triton), CSNU (COSCO), HLCU (Hapag-Lloyd), and MSCU (MSC). It identifies registered equipment ownership or operation, not necessarily the shipping line for a particular journey.
The Equipment Category (4th Letter)
"U" stands for freight container — the standard intermodal box used for cargo. You may also see "J" for detachable freight container-related equipment, or "Z" for trailers and chassis. In practice, nearly all containers you will track as an importer or exporter use "U".
The Serial Number and Check Digit
The 6-digit serial number uniquely identifies the container within the owner's fleet. The final check digit is calculated from the preceding 10 characters using an algorithm — it lets computer systems verify the number was entered correctly and catch typos before they cause costly misrouting.
Container Number vs Bill of Lading vs Booking Reference
These three references are often confused. A container number identifies the physical steel box. A bill of lading (B/L) is a legal document number issued by the carrier for a specific shipment — one B/L can cover multiple containers. A booking reference is a reservation number issued before the cargo is loaded. Choose the matching reference type and the shipping line. Not every carrier or data source accepts every reference type.
How to Track Your Container on Trackora
Paste your ISO 6346 container number directly into the Trackora search box. Confirm the shipping line from your booking or B/L: the equipment owner prefix does not necessarily identify the line carrying this shipment. Select that carrier in Trackora. Available event data depends on the connection; use the official portal if no events are returned.