The smart container number checker.
A container's check digit is the 11th character, and it is calculated from the first ten. Each letter gets a number (A=10, B=12, C=13 … the values skip 11, 22 and 33), and each digit keeps its own value. Each value is multiplied by 2 raised to its position (1, 2, 4 … 512). Add them up, divide by 11, and the remainder is the check digit (a remainder of 10 counts as 0). Type the number below and this calculator does the math, shows the correct check digit, and, if the number fails, tests one-character misreads like O↔0 or B↔8. A pass means the number is consistent, not that the container is registered or in your yard. The owner-code register is kept by BIC. Runs in your browser, no signup, no upload.
Example: CSQU305438 → 13·1 + 30·2 + 28·4 + 32·8 + 3·16 + 0·32 + 5·64 + 4·128 + 3·256 + 8·512 = 6185. 6185 mod 11 = 3, so CSQU3054383 is valid.
Why does a scanned container number fail validation?
Most failures are not bad containers, they are misread characters. O read as 0, I as 1, B as 8, S as 5, and Z as 2 are the common ones, and any single swap breaks the ISO 6346 check digit. This checker runs the math, then tests one-character corrections at the positions where each confusion is possible and reports the likely intended number.
Why a checker that fixes, not just flags.
A container number is four letters and seven digits, and that final digit is a modulo-11 check digit computed from the first ten characters. When a scanner misreads a single character — a faded 0 read as O, a rusted 8 read as B — the check digit no longer matches and the number is rejected. A plain validator stops there. In a real yard, that means a clerk re-typing under pressure, or a wrong number slipping into the gate log.
Step 1 — Validate
The eleventh digit is recomputed from the first ten characters using the ISO 6346 modulo-11 formula and compared to what you typed. Match means the number is internally consistent.
Step 2 — Auto-correct
If it fails, the checker tries a single-character repair on the confusables OCR mistakes most — O↔0, I↔1, B↔8, S↔5, G↔6, Z↔2, A↔4 — keeping the first four positions letters and the last seven digits, then re-validates. One clean candidate is shown as the likely correct number.
The same check runs inside the Vantage app.
The auto-correct above is one taste of what Vantage does automatically. In the iPhone app, Vantage reads trailer and container numbers from a photo; container numbers also get the ISO 6346 check digit and a one-character repair when only one fix passes it; the clerk confirms every read.
Photo, not typing.
A clerk photographs the number from a phone. Works offline in the iPhone app, no kiosks, no fixed cameras at the gate.
Checked before it lands.
Container reads are checked against the ISO 6346 check digit and single-character misreads are auto-corrected; the clerk confirms every read before it is saved.
Fewer typos in the gate log.
The clerk checks each read at the gate, not three hours later in the yard.
Run the whole pipeline on a phone.
Vantage YMS — free plan with no card, paid plans from $149/mo, no setup fee.
Frequently asked
How is a container check digit calculated?
A container's check digit is the 11th character, and it is calculated from the first ten. Each letter gets a number (A=10, B=12, C=13 … the values skip 11, 22 and 33), and each digit keeps its own value. Each value is multiplied by 2 raised to its position (1, 2, 4 … 512). Add them up, divide by 11, and the remainder is the check digit (a remainder of 10 counts as 0). Example: CSQU305438 gives 13·1 + 30·2 + 28·4 + 32·8 + 3·16 + 0·32 + 5·64 + 4·128 + 3·256 + 8·512 = 6185, and 6185 mod 11 = 3, so CSQU3054383 is valid. The ISO 6346 owner-code register is kept by BIC.
Why is there no 11, 22 or 33 in the letter values?
Those values are multiples of 11, and in a mod-11 check they would act like 0. So the letter scale skips them: A=10, B=12 … K=21, L=23 … U=32, V=34 … Z=38.
What if the remainder is 10?
The check digit is written as 0. This calculator applies that rule automatically.
Can Vantage read the container code from a photo?
Yes, in the Vantage iPhone app. A clerk photographs the number, container numbers get the ISO 6346 check and a one-character repair when only one fix passes, and the clerk checks the read before it is saved. On the Free plan the reading runs on the iPhone itself; Lite and up add cloud AI reading (Lite up to 1,000 a month). The Android app is live on Google Play (an update fixing Google sign-in is on its way) and does Gate IN/OUT; photo reading is in the iPhone app. Free plan: $0, no card, 3 users, 1 yard. Paid plans from $149/mo.
Container nummer check: does it work for any shipping line?
Yes, for any ISO 6346 sea container number: 4 letters (a 3-letter owner code plus U, J or Z), then 6 serial digits and 1 check digit. The owner code tells you the line or lessor, and BIC keeps that register.
Does this fix OCR misreads in a container number?
Yes. If a number fails the ISO 6346 check digit, the checker tries a single-character repair on the visual confusions OCR makes most — O↔0, I↔1, B↔8, S↔5, G↔6, Z↔2, A↔4 — keeping the first four positions letters and the last seven digits, then re-validates. If exactly one corrected candidate passes the check digit, it's shown as the likely correct number. The Vantage iPhone app runs the same check on every container number it reads from a photo.
Does it run in my browser?
Yes. The checker runs entirely in your browser in JavaScript. Nothing is uploaded, logged, or stored — you can disconnect your network and it will still validate and auto-correct.
A valid check digit means the container is real, right?
Not necessarily. A valid check digit confirms the number is internally consistent, not that it belongs to a real, registered container. Vantage YMS pairs this with your appointment data so a valid-but-unexpected container gets flagged at the gate, not after the fact.
Does this work for trailer numbers and US domestic intermodal?
This checker covers ISO 6346 sea/ocean containers (four letters, seven digits). Vantage YMS itself reads container numbers, trailer numbers, license plates, and chassis numbers — but that's a job for the app, not this tool. Just need the check digit on a clean number? Use the basic calculator.
The other free tools
Receiving containers from a drayage carrier? What an EIR (Equipment Interchange Receipt) is, and what to log at your own gate.
Put this checker on your own site
Free to embed on any site, no permission or attribution needed beyond the small credit line inside the widget. It loads a stripped-down view with no header, no footer, and no marketing.
Stop re-typing misread numbers.
Vantage YMS — free plan with no card, paid plans from $149/mo. Cancel anytime.