Free container tools
Container number checker
Check a container number against ISO 6346, or get the missing check digit.
ISO 6346 · 10 or 11 characters
What each part of the number means
A container number starts with a three-letter owner code, followed by the equipment category: U for a freight container, J for detachable equipment, or Z for a trailer or chassis. The next six digits are the serial number. The eleventh character is the check digit.
How the check digit works
ISO 6346 gives each letter a numeric value, skipping multiples of 11. Each of the first ten values is multiplied by a power of two, starting at 1 on the left and ending at 512. Divide the sum by 11: the remainder is the check digit, except that a remainder of 10 becomes 0. This checks the number, not the registration or ownership of the container.
Frequently asked questions
What is a container check digit?
It is the final digit of an ISO 6346 container number. It is calculated from the preceding ten characters to help detect typing and transcription errors.
Why does my container number fail the check?
The number may contain a mistyped owner code, category, serial number or check digit. A valid check digit does not prove that the container exists or that its owner code is registered.
What does the U in a container number mean?
U identifies a freight container. J identifies detachable container-related equipment, and Z identifies a trailer or chassis.
Can I check many container numbers at once?
Yes. Check a list accepts up to 1,000 numbers separated by lines, commas or spaces. You can copy the invalid numbers or download all results as CSV.
Run this in Krak Stack
Krak Stack checks every container number when you create a container, import your stock or record a pickup.