Container check digit calculator
Type the first 10 characters of a container number to get its check digit, or all 11 to see whether the number is valid. The calculation follows ISO 6346 and runs in your browser; nothing is sent anywhere.
How the check digit is calculated
A container number has four letters (three for the owner, one for the equipment category, usually U) followed by six serial digits and one check digit. The check digit catches most typing errors:
- Each letter is converted to a number: A = 10, B = 12, C = 13 … Z = 38. Values that are multiples of 11 (11, 22, 33) are skipped.
- Each of the first ten characters is multiplied by 2 to the power of its position: 1, 2, 4, 8 … 512.
- The products are added up and divided by 11. The remainder is the check digit; a remainder of 10 counts as 0.
Worked example: CSQU 305438
| 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 products add up to 6,185. 6,185 ÷ 11 leaves a remainder of 3, so the full number is CSQU 305438 3.
Letter values
| A 10 | B 12 | C 13 | D 14 | E 15 | F 16 | G 17 | H 18 | I 19 |
| J 20 | K 21 | L 23 | M 24 | N 25 | O 26 | P 27 | Q 28 | R 29 |
| S 30 | T 31 | U 32 | V 34 | W 35 | X 36 | Y 37 | Z 38 |
Why it matters in operations
A single wrong digit in a container number means tracking returns nothing, an arrival notice goes out with the wrong equipment, or a trucker is sent for the wrong box. Checking the digit when a number is first typed or read from a document stops these errors before they reach the customer. WardOps checks the digit of every container number it reads from a bill of lading or arrival notice and files only the numbers that pass.
FAQ
Does a valid check digit mean the container exists?
No. It only means the number is well formed. A mistyped number can still pass by chance, and a valid number may belong to a container that is not on your shipment. Confirm against the bill of lading or the carrier's tracking.
What do the four letters mean?
The first three letters are the owner code, registered with the Bureau International des Containers (BIC). The fourth is the equipment category: U for freight containers, J for detachable freight container equipment and Z for trailers and chassis.
Why is there no 11, 22 or 33 in the letter values?
The calculation divides by 11, so a letter worth 11, 22 or 33 would add nothing to the remainder and a mistake in that letter would go unnoticed. Skipping those values keeps every letter counted.