Every shipping container in the world carries a unique 11-character identification code stamped on its doors, sides, and roof. This number follows the ISO 6346 standard and encodes the container’s owner, type, unique serial number, and a check digit for validation. Once you know how to read it, you can extract meaningful information from any container number in seconds.
The 4 Parts of a Container Number
Part 1: Owner Code (3 Letters)
The first three letters identify the container’s registered owner. These three-letter codes must be registered with the BIC (Bureau International des Containers), headquartered in Paris, which maintains the global registry. Examples:
- MSK — A.P. Møller-Maersk (the “MSK” is Maersk Line’s owner code)
- MSC — Mediterranean Shipping Company
- HLC — Hapag-Lloyd Container
- TRI — Triton International (the largest container leasing company)
- TEX — Textainer Equipment Management
Part 2: Category Identifier (4th Letter)
The fourth character identifies the type of equipment. There are three possible values:
- U — Freight Container (the vast majority — every standard dry, reefer, open top, and flat rack)
- J — Detachable freight container-related equipment (generator sets, clip-on units)
- Z — Trailer and semi-trailer chassis (not technically a container but tracked in the same system)
In practice, almost every container you encounter will have “U” as the fourth character.
Part 3: Serial Number (6 Digits)
The next six digits are a serial number assigned by the owner. Serial numbers are assigned sequentially or semi-randomly. If the number has fewer than 6 significant digits, it is padded with leading zeros (e.g., the number “55” becomes “000055”). The combination of Owner Code + Category Identifier + Serial Number is globally unique — no two containers in the world have the same combination.
Part 4: Check Digit (Final Single Number)
The 11th character is a mathematically calculated check digit, shown in a small box on the container door panel. It is calculated by assigning each letter and digit a numerical value, multiplying by powers of 2, summing the results, and taking the remainder when divided by 11. If the check digit does not match the calculation, the container number contains an error. Tracking systems that implement check digit validation will immediately flag a mistyped container number, saving time in logistics operations.
Bonus: ISO Size Type Code
Below the main container number, containers carry an ISO Size Type Code — a 4-character code providing size and type information at a glance:
- First character = Length: 2 = 20 ft, 4 = 40 ft, L = 45 ft
- Second character = Height and width: 2 = standard 8’6″, 5 = high cube 9’6″
- Last two characters = Type: G1 = General Purpose (dry), R1 = Reefer, T1 = Tank, P1 = Flat Rack/Platform
Examples: 22G1 = 20-foot standard dry container; 45G1 = 40-foot high cube dry; 45R1 = 40-foot high cube reefer; 22T1 = 20-foot tank container; 42P1 = 40-foot flat rack.
Bottom Line
Reading a container number is a skill every logistics professional should have. The owner code tells you who owns or operates the box. “U” confirms it’s a freight container. The 6 serial digits make it unique. And the check digit lets any computer instantly detect a transcription error. Next time you see a container, you can decode its full identity in under 10 seconds. Enter any container number on TraceContainer.com to start tracking instantly.