Container number check digit (ISO 6346): how it works, with a calculator
Updated
Every shipping container number ends in a check digit that catches most typing errors. Here is how it is calculated, and a calculator to check yours.
4 letters and 6 or 7 digits, for example CSQU3054383
Check digit: 3Valid container number
| C | S | Q | U | 3 | 0 | 5 | 4 | 3 | 8 |
| 13 | 30 | 28 | 32 | 3 | 0 | 5 | 4 | 3 | 8 |
| 1 | 2 | 4 | 8 | 16 | 32 | 64 | 128 | 256 | 512 |
Sum 6185 ÷ 11 → remainder 3
The structure of a container number
| Part | Example | Meaning |
|---|---|---|
| Owner code | CSQ | Three letters registered with the BIC (Bureau International des Containers) |
| Category identifier | U | U = freight container, J = detachable freight-container equipment, Z = trailer or chassis |
| Serial number | 305438 | Six digits chosen by the owner |
| Check digit | 3 | Calculated from the first ten characters |
How the check digit is calculated
- Convert each letter to a number: A = 10, then B = 12 … Z = 38. Multiples of 11 (11, 22, 33) are skipped, so the values run A 10, B 12 to K 21, L 23 to U 32 and V 34 to Z 38.
- Digits keep their own value.
- Multiply each of the first ten values by 2 to the power of its position: 1, 2, 4, 8 … 512.
- Add the products and take the remainder after dividing by 11. A remainder of 10 becomes 0.
Worked example for CSQU3054383:
| Character | 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 |
The sum is 6,185, and 6,185 ÷ 11 = 562 remainder 3. The check digit is 3, so CSQU3054383 is valid.
Why it matters
A single wrong letter or digit, or two swapped digits, almost always changes the check digit. Checking it before the shipping instruction goes to the carrier catches typos that would otherwise be printed on the bill of lading, the customs declaration and the insurance certificate. See also what must match between the invoice, packing list and B/L.
How LADEO helps
When LADEO reads a bill of lading it validates the check digit of every container number, pairs each container with its seal number and fills them into the shipment's logistics record.