Container Check Digit Calculator

Calculate or verify the ISO 6346 check digit of shipping container numbers. Paste one number or a list from a gate log or spreadsheet, and see which ones fail and what they were most likely meant to be.

2 of 3 valid
  • CSQU3054383Valid

    Owner CSQ · Category U · Serial 305438 · Check digit 3

  • MSKU1234565Valid

    Owner MSK · Category U · Serial 123456 · Check digit 5 (calculated)

  • TGHU8763210Check digit fails

    Owner TGH · Category U · Serial 876321 · Check digit 0

    The number calls for check digit 7, not 0. Similar-looking numbers that pass: TGHU0763210, TGHU8763710, TGHU8763270. Confirm against the container before using one.

Calculated in your browser; nothing is uploaded and no credits are used.

When a scanned number fails the check

Gate cameras and OCR read container numbers from paint that is often rusty, dented or partly hidden. A failed check digit is the signal that one character is wrong, so a gate system should not accept it silently. A workable rule:

  1. Accept numbers that pass the check digit.
  2. Match a failing number against the expected containers (booking, pre-advice or yard inventory). If exactly one expected number is a similar-looking reading, use it.
  3. Retake another frame or the other side of the container when the camera can.
  4. Route the rest, with the image, to an operator.

The Container OCR API returns the number with is_valid and the parsed owner code, category, serial and check digit, so this rule takes a few lines of code. See the gate camera integration, or read a number from a photo with the free container scanner.

Frequently asked questions

How is the container check digit calculated?
Each of the first 10 characters gets a value: digits keep their value, and letters run from A = 10 to Z = 38, skipping multiples of 11 (so B = 12, L = 23, V = 34). Multiply each value by 2 to the power of its position (1, 2, 4, … 512), add them up, divide by 11 and take the remainder. A remainder of 10 becomes 0.
What does a failed check digit mean?
At least one character was misread or mistyped, usually a digit that looks like another (8 and 0, 6 and 5, 1 and 7) or the check digit itself, which is often printed in a box and can be missed. It can also be a genuinely wrong number painted on the container, which is rare.
Are the suggested numbers correct?
They are numbers one similar-looking character away that pass the check. More than one can pass, so treat them as candidates and confirm against the container, the booking or a second photo.
Can I check numbers without the check digit?
Yes. Enter the 10-character owner code, category and serial number, and the calculator adds the check digit.
Is anything uploaded?
No. The calculation runs in your browser and nothing you type is sent to a server.