Every shipping container carries an eleven character identity under ISO 6346. It is not an arbitrary serial number. The last digit is a check digit computed from the other ten, which means you can tell a mistyped container number from a real one without asking anybody.
That is more useful than it sounds. A transposed digit in a container number sends the wrong box onto a customs entry, breaks tracking, and is one of the more tedious errors to unpick after the fact.
The four parts
Take CSQU 305438 3:
- CSQ is the owner code, three letters, registered with the Bureau International des Containers in Paris.
- U is the equipment category identifier. U means a freight container, J means detachable freight container related equipment, Z means a trailer or chassis. Almost everything you handle is U.
- 305438 is the six digit serial number, assigned by the owner.
- 3 is the check digit.
Verifying the check digit by hand
Each letter has a numeric value starting at A equals 10, running through the alphabet, skipping every multiple of 11. So A is 10, B is 12, C is 13, and there is no letter worth 11, 22 or 33.
Each of the first ten positions is multiplied by a weighting of 2 to the power of its position minus one: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512. Sum the products, divide by 11, and the remainder is the check digit. A remainder of 10 is written as 0.
Worked through for CSQU3054383:
- C is 13, times 1, equals 13
- S is 30, times 2, equals 60
- Q is 28, times 4, equals 112
- U is 32, times 8, equals 256
- 3 times 16 equals 48
- 0 times 32 equals 0
- 5 times 64 equals 320
- 4 times 128 equals 512
- 3 times 256 equals 768
- 8 times 512 equals 4096
The total is 6185. Divided by 11 that is 562 remainder 3, and 3 is the printed check digit. The number is valid.
The size and type code
Below or beside the number sits a four character code describing the box itself. In 45G1, the first character is length (4 means 40 foot), the second is height and width (5 means 9 foot 6, a high cube), and the last two are the type (G1 is a general purpose container with vents). R is reefer, T is tank, U is open top, P is platform or flat rack.
This is the code that tells you whether you have been given a standard box or a high cube when the paperwork just says forty foot. If you are still choosing equipment, see container types and dimensions.
The CSC safety approval plate
On the door you will find a metal plate required by the International Convention for Safe Containers 1972. It is a structural certificate, and a container without a valid one should not be moving. It carries:
- Country of approval and the approval reference
- Date of manufacture and the manufacturer's identification number
- Maximum operating gross mass, the heaviest the box may ever be, cargo plus tare
- Allowable stacking weight at 1.8g, which is how many loaded boxes may sit on top of it at sea
- Transverse racking test force
The plate also shows how the container is kept in survey: either a next examination date, or an ACEP number, meaning the owner runs an Approved Continuous Examination Programme and inspects on a schedule rather than to a stamped date.
Check the maximum gross mass against what you intend to load. It is a legal ceiling for the container, and it is a different number from the road weight limit that will actually stop your delivery, which is usually lower. Your VGM figure must never exceed it.
What to do when the number does not check out
- Re-read the box, not the email. Most failures are transcription errors between the depot and the booking.
- Check the owner code exists. The BIC register is public, and a code that is not registered is a red flag on a container you have been offered.
- Fix it before the bill of lading is issued. Correcting a container number after the manifest has gone to customs means an amendment, a fee and, in some ports, a delay.
