ISO 6346 Container Number Validator & Size/Type Decoder
Check whether a container number is arithmetically valid, see the check digit recalculated step by step, and decode the 4-character size/type code stamped next to it. Everything runs in your browser — nothing is uploaded.
You have the owner code and the six serial digits but the last digit is unreadable on the door. Enter the first 10 characters and the correct check digit is calculated for you.
The four characters under or beside the container number describe its length, height and build — not its contents. Enter a code such as 22G1, 45R1 or 22T6.
| Code | Equipment | Nominal length | Outside height |
|---|
Nominal lengths and heights follow the standard ISO 668 series. Always read the container's own CSC safety approval plate for its actual tare, payload and maximum gross mass — those vary by build, not by code.
What an ISO 6346 container number is
Every shipping container carries an 11-character identity that is unique worldwide for the life of the box. ISO 6346 is the international standard that fixes its shape: three letters for the owner, one letter for the equipment category, six digits of serial number, and one final digit that exists only to prove the other ten were copied down correctly. You will see it on the doors, on both sides, on the roof and on the paperwork, and every party in the chain — carrier, terminal, customs, your forwarder — keys on it.
- Owner code — 3 letters. Identifies the container's owner or principal operator. Codes are registered with the Bureau International des Containers (BIC) in Paris; an unregistered code is a red flag even when the arithmetic passes.
- Category identifier — 1 letter. Only three values are legitimate: U for all freight containers, J for detachable freight-related equipment, Z for trailers and chassis. In practice almost everything you handle is U.
- Serial number — 6 digits. Assigned by the owner. It carries no meaning you can decode; consecutive numbers do not imply similar boxes.
- Check digit — 1 digit. Calculated from the first ten characters. It catches typing errors, not fraud.
- Each of the four letters is converted to a number, starting A = 10 and counting upwards, but skipping every multiple of eleven. That is why L is 23 rather than 21, and why no letter is ever worth 11, 22 or 33.
- Each of the ten characters is multiplied by a weight that doubles as you move right: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512.
- The ten products are added together and divided by 11. The remainder is the check digit.
- A remainder of 10 is written as 0. This is the one case where the digit does not uniquely identify its remainder, and it is why roughly one number in eleven cannot be fully verified by arithmetic alone.
Use the validator above and it prints every multiplication, so you can check the maths by hand if a terminal disputes your number.
What a valid number does not tell you
This is where costly assumptions are made. A number that passes the check-digit test is only internally consistent. It does not prove the container exists, that it is seaworthy, that the owner code is registered, or that the box is the one named on your bill of lading. It tells you nobody mistyped it.
- That the owner code is real. Look it up in the BIC's free public register rather than assuming a plausible four-letter prefix belongs to a carrier.
- That the box is fit to travel. The CSC safety approval plate on the door carries the approval date and next examination date. An expired plate can stop a container at a port gate regardless of how correct its number is.
- That the number matches your documents. Compare the number on the box, on the packing list, on the bill of lading and on the customs declaration. A single transposed digit between documents is one of the commonest causes of a discrepancy under a letter of credit.
Reading the size and type code
Next to the identity number sits a separate four-character code that describes the hardware. The first character gives nominal length, the second gives height and width, and the last two describe the type of container and a variation within that type. So 22G1 is the ordinary 20-foot dry box that most quotations assume, 42G1 its 40-foot equivalent, 45G1 a 40-foot high cube, and 45R1 a 40-foot high-cube reefer.
Two traps are worth naming. First, the height character is easy to misread: 2 means the standard 2,591 mm box and 5 means the 2,896 mm high cube, a difference of about 30 cm of usable stacking height that changes how many of your cartons fit. Second, the code says nothing about payload. Two containers with identical 22G1 codes can have tare weights differing by a hundred kilograms or more, which matters when you are close to a road weight limit.
- Confirmed which box you have? Check its full specification in the Container Standards Library.
- Planning how much fits inside it: the 3D Container Stuffing Calculator and the 3D Pallet Calculator.
- Shipping a reefer code such as 45R1? Set the carriage temperature from the Reefer Cargo Temperature Guide.
- Costing the shipment end to end: the Landed Cost Estimator.
Frequently asked questions
Nearly always a reading error rather than a bad container. The usual culprits are 0 read as O, 1 read as I, 5 read as S, 8 read as B, and two adjacent digits swapped. Re-read the number from the door end, where it is stencilled largest, and try again.
They should not. The owner code is registered to one operator and the serial is theirs to allocate, so the combination is unique while the box is in service. Numbers can in principle be reissued long after a container is scrapped, which is one reason archived shipment records should always keep the date alongside the number.
No. Anyone can construct a number whose arithmetic is correct. The check digit is a transcription safeguard. To establish that a container genuinely belongs to the operator named, verify the owner code in the BIC register and confirm the booking with the carrier directly.
Both describe a standard 20-foot dry container, but they come from different editions of the coding scheme. The four-digit form such as 2200 or 4200 belongs to the older numeric series still seen on long-serving boxes and in some carrier systems; the alphanumeric form such as 22G1 or 42G1 is the current one. Where a booking system accepts only one form, use the one it asks for and note the other on your file.
No. It is a free independent calculator written by IMPUTIX that implements the publicly documented check-digit arithmetic and code structure. It is not published, endorsed or certified by ISO or by the Bureau International des Containers, and it does not reproduce the text of the standard. For the authoritative wording, buy ISO 6346 from ISO or a national standards body.
Reference information for planning purposes only. Container specifications vary by build and by operator; the container's own CSC plate and your carrier's booking confirmation govern.