How a container number is built
An ISO 6346 number consists of:
- 3 letters: owner code
- 1 letter: equipment category (U freight container, J detachable equipment, Z trailer/chassis)
- 6-digit serial number
- 1 check digit
How the check digit is found
Letters map to numbers starting at A=10, skipping multiples of 11. Each of the first 10 characters is multiplied by 2 to the power of its position (0 to 9) and summed. Divide the sum by 11; the remainder is the check digit (a result of 10 becomes 0).
Example: CSQU305438
C=13, S=30, Q=28, U=32. The products are 13, 60, 112, 256, 48, 0, 320, 512, 768, 4096.
sum = 6185; 6185 mod 11 = 3
The check digit is 3, so the number is CSQU3054383.
Tip
Mistyped numbers cause booking and tracking errors, so validate the number before you book.
The calculator does this for you: when you type a number whose last digit is wrong, it warns you. The check only catches typing errors; it does not show that the container actually exists or what its status is.
