Free tool
Container number check
An ISO 6346 container number has 11 characters: a 3-letter owner code, a category letter (U, J or Z), a 6-digit serial number and a check digit calculated from the first 10. A wrong check digit almost always means a typing error.
Results
- CSQU3054383✓ Valid
- Owner
- CSQ
- Category
- U · freight container
- Serial
- 305438
- Check digit
- 3
Show the calculation
Char. Value × Weight = Product C 13 1 13 S 30 2 60 Q 28 4 112 U 32 8 256 3 3 16 48 0 0 32 0 5 5 64 320 4 4 128 512 3 3 256 768 8 8 512 4096 Sum 6185 ÷ 11 = remainder 3 → digit 3
- MSBU8981485✗ Invalid
Wrong check digit: 5 found, 8 expected. Possible corrected number: MSBU8981488.
- Owner
- MSB
- Category
- U · freight container
- Serial
- 898148
- Check digit
- 8
Show the calculation
Char. Value × Weight = Product M 24 1 24 S 30 2 60 B 12 4 48 U 32 8 256 8 8 16 128 9 9 32 288 8 8 64 512 1 1 128 128 4 4 256 1024 8 8 512 4096 Sum 6564 ÷ 11 = remainder 8 → digit 8
How the check digit is calculated
- 1Each letter has a value: A = 10, B = 12, C = 13… skipping 11, 22 and 33 (multiples of 11). Digits keep their own value.
- 2Each character is multiplied by a weight that doubles at every position: 1, 2, 4, 8… up to 512 for the 10th character.
- 3Add the ten products and divide the sum by 11. The remainder is the check digit — a remainder of 10 gives 0.
Example: CSQU305438
| Char. | C | S | Q | U | 3 | 0 | 5 | 4 | 3 | 8 |
|---|---|---|---|---|---|---|---|---|---|---|
| Value | 13 | 30 | 28 | 32 | 3 | 0 | 5 | 4 | 3 | 8 |
| × Weight | 1 | 2 | 4 | 8 | 16 | 32 | 64 | 128 | 256 | 512 |
| = Product | 13 | 60 | 112 | 256 | 48 | 0 | 320 | 512 | 768 | 4096 |
Sum 6185 ÷ 11 = remainder 3 → digit 3 → CSQU3054383
Why it matters before customs clearance
The container number links the physical box, the carrier's manifest, the bill of lading and the customs declaration. One digit copied wrongly on any of these documents is enough to create a discrepancy that customs or the terminal will have to clear.
The check digit catches most typing errors and swapped digits. It does not prove that the container exists or that it is yours: for that, the number has to be compared across every document of the shipment.
FAQ
What is a container number check digit?+
It is the 11th and last character of the number. It is calculated from the first 10 according to ISO 6346: each character's value multiplied by a power of 2, the sum divided by 11, the remainder giving the digit (10 becomes 0). It detects typing errors.
What does the 4th letter mean?+
It is the equipment category identifier: U for a freight container, J for detachable freight container-related equipment, Z for a trailer or chassis. A number whose 4th letter is not U, J or Z is not a valid container number, even if its check digit happens to match.
Does a valid number prove it is the right container?+
No. A correct check digit only proves the number is well formed. You still need to check that the same number appears on the shipment's packing list, House B/L and Master B/L, with the same seal.
What should I do if the check digit is wrong?+
Go back to the source document or a photo of the container. The tool suggests the number with a recalculated check digit, but the error may be in another position: do not correct a document without checking the source.
Are the numbers I enter stored?+
No. The calculation runs in your browser; no number is sent to our servers.
What about the whole shipment?
ClearBerth checks the container number, seal, weights, packages and EUR.1 across the packing list, House B/L and Master B/L — and names the document to correct.
Free trial — 5 shipments