Container number check digit calculator
This container number validator checks the ISO 6346 check digit of any container number and shows exactly how it is calculated. Free, and it runs in your browser: nothing you type is sent anywhere.
How the check digit is calculated
- Convert each character. Digits keep their value. Letters become numbers: A = 10, then counting up while skipping 11, 22 and 33 (so K = 21, U = 32, Z = 38).
- Weight by position. Multiply the first character by 1, the second by 2, then 4, 8 and so on up to 512 for the tenth.
- Divide by 11. Add the ten products and take the remainder after dividing by 11.
- Read the digit. The remainder is the check digit. A remainder of 10 is written as 0.
Reading a container number
- MSK
- Owner code. Three letters registered with the BIC, identifying who owns the container.
- U
- Equipment category. U for freight containers, J for detachable equipment, Z for trailers and chassis.
- 447102
- Serial number. Six digits the owner assigns to the individual container.
- 5
- Check digit. Calculated from the ten characters before it, so typing mistakes show up.
Owner prefixes for the lines we cover are listed on our carrier pages.
Check a whole list
Paste up to 500 numbers, one per line or separated by commas, to find the mistyped ones before they reach a booking or a tracking tool.
Questions about container numbers
What is a container number?
A container number is an 11-character code defined by ISO 6346: a three-letter owner code, a one-letter equipment category, a six-digit serial number and a check digit. It is painted on the container doors and roof and printed on the bill of lading.
What does the check digit do?
The eleventh character is calculated from the first ten. If one character is mistyped, the calculated digit usually no longer matches, so the mistake is caught before the number is used.
How is the check digit calculated?
Each letter is converted to a number (A = 10, then counting up while skipping 11, 22 and 33), each digit keeps its value, and each value is multiplied by 2 raised to its position (1, 2, 4 and so on up to 512). The total is divided by 11; the remainder is the check digit, and a remainder of 10 is written as 0.
What do U, J and Z mean in a container number?
The fourth letter is the equipment category: U for freight containers, J for detachable freight-container equipment and Z for trailers and chassis. Almost every shipping container you track has a U in fourth place.
Does a valid number mean the container is in transit?
No. A valid check digit means the number is correctly formed; it does not confirm that the container exists or where it is. To see the vessel carrying it and a predictive ETA, track it with ShipTastic.
Is the number I type sent to ShipTastic?
No. The check runs entirely in your browser. The number is only used to find a voyage if you choose to track the container.
Guide: How to read a container number (ISO 6346) · More free tools