How to use the container number validator (iso 6346)
- Paste the container numbers, one per line. Spaces and hyphens are ignored and letters can be in either case.
- Use 11 characters to test a number, or 10 characters to have the last digit worked out.
- Read the result for each line: whether the check digit works, the weighted sum, the sum mod 11 and the digit that would be needed.
- Look at the last column for the three owner letters and the equipment letter, then copy the table or download the CSV.
Formula
letter values: A = 10, B = 12, C = 13, and so on, skipping 11, 22 and 33
sum = c1 x 1 + c2 x 2 + c3 x 4 + ... + c10 x 512
check digit = (sum mod 11) mod 10
Each of the first ten characters is multiplied by a power of two, from 1 for the first to 512 for the tenth. Letters skip the multiples of 11 because those would share a factor with the divisor 11. A remainder of 10 is written as 0.
Checking CSQU3054383
The letters C, S, Q and U have the values 13, 30, 28 and 32, and the digits are 3, 0, 5, 4, 3 and 8. Multiplying by 1, 2, 4, 8, 16, 32, 64, 128, 256 and 512 gives 13, 60, 112, 256, 48, 0, 320, 512, 768 and 4,096. They add up to 6,185.
Dividing 6,185 by 11 gives 562 with a remainder of 3, so the expected check digit is 3, which matches the last character. Change the last digit to 4 and the page reports that the check digit fails and that the last digit would be 3.
The parts of a container number
A container number has three parts before the check digit: three letters for the owner code, one letter for the equipment category, and six digits for the serial number. The category letter is usually U for a freight container, J for detachable equipment such as a generator and Z for a trailer or chassis.
The page shows the owner code and the category letter for each number so you can see whether a typed number at least has the right shape. It cannot tell you who owns a container today.
What the check does and does not prove
The weighting catches almost every single wrong character and most swapped neighbors, so a failing number has almost always been mistyped. Because the divisor is 11, about one in ten random numbers of the right shape also passes by chance.
A passing number is consistent, nothing more. Confirm the number against the bill of lading, the seal record or the shipping line before you act on it. For vehicles use the VIN Check Digit Validator.
Assumptions and limits
- The standard layout of four letters, six digits and a check digit is expected. Numbers in another layout are refused with a message.
- The page checks arithmetic only. It looks nothing up and does not know who owns a container.
- The equipment letter is shown with the usual meaning of U, J or Z. Other letters are reported as not one of those three.
- Up to 200 lines are read at once.
- Nothing typed here leaves your browser.
Frequently asked questions
Why are 11, 22 and 33 skipped in the letter values?
The check is a remainder after dividing by 11. A letter worth a multiple of 11 would add nothing to that remainder, so the letter values step over those numbers and every letter makes a difference.
What happens when the remainder is 10?
The check digit is written as 0, because only a single digit fits. That is the one case where two different remainders, 0 and 10, give the same last digit.
Does a valid number mean the container exists?
No. The arithmetic only shows that the characters agree with each other. Owners and numbers are tracked by the shipping industry, and the page makes no lookups.
Can I test a number without its last digit?
Yes. Enter the first ten characters on a line of their own and the page returns the full 11 character number with the check digit added.