CargoFlowPlus
Check a container number
Paste a container number to confirm its format and check digit, see who owns the prefix and find the right place to track it. Free, no sign-up.
- ISO 6346 check digit
- Prefix owner lookup
- No sign-up needed
How a container number is built
A container number has four letters and seven digits. The first three letters are the owner code, the fourth is the equipment category (U for freight containers), the next six digits are the serial number and the last digit is a check digit.
Why the check digit matters
The check digit is calculated from the first ten characters. A mistyped character will often make the calculation fail, so checking the digit can help spot a wrong number before it reaches a carrier search, a customs entry or a haulier booking.
What the prefix does and does not tell you
The owner code identifies a registered owner or principal operator. It does not prove who owns a particular box or who is carrying your shipment. Leased boxes and slot agreements mean the carrier on your booking or bill of lading is the one to track with.
How CargoFlowPlus handles it
- Paste the number: Spaces, dashes and lower case are fine; the checker cleans them up.
- Read the result: See whether the check digit is right, which digit it should be, and who owns the prefix.
- Track it: Open the carrier guide, or add the container to CargoFlowPlus to follow ETA changes and free time.
How is the container check digit calculated?
Each of the first ten characters gets a value (letters from 10 to 38, skipping multiples of 11; digits keep their value), multiplied by 2 to the power of its position. The sum is divided by 11 and the remainder is the check digit, with 10 counted as 0.
Does a valid check digit mean the container exists?
No. It only shows the number is internally consistent. A valid number can still be wrong for your shipment, so compare it with your booking, bill of lading or packing list.
Official sources
Sources checked . Carrier tools and access conditions may change.