Every one of the 34.5 million containers in the global fleet has a unique identifing number of four letters and seven digits - each of which tells you something about the container. Want to know how to crack the code? See our previous post on what makes up a shipping container number.

The final digit in a container number is something called a check digit number. It's used to confirm that a container number was properly transferred or recorded for container tracking, handling, and storage. Here's how the check digit number is generated. 

Let's use container number TEMU6284450 as an example.

To start, the letters of the alphabet are assigned a numerical value starting with 10. Multiples of 11 aren't used here - they have a special role later on. 

Now we have numberical values for the letters. The registration numbers are their own values, and the final number 0 is the check digit number (which we don't use in the calcuation).

Step 1: Multiply the values by all powers of 2 and add the results. In our example, we get 5,181 as the total.

Step 2: Divide the sum by 11. If your result contains decimals, just ignore them. For our number, 5,181 divided by 11 is 471.

Step 3: Multiply your result by 11.  We get 5,181.

Step 4: Subtrack the result of step 3 from the result of step one to get your check digit number.

Our final number is 0, which matches the check digit number. Hooray! Everything checks out.

If you want to know whether your container is available for pickup at the terminal, that's another story. Sign up for a free Crux Systems container tracking account and get real-time container location and status information for all of your containers in one place.