Container Number Validator
ValidatorValidate ISO 6346 shipping container numbers. Decodes the owner code, equipment category, and serial number, and recomputes the mod-11 check digit. Runs entirely in your browser.
About this tool
About Container Number Validator
A shipping container number is an 11-character code, standardized by ISO 6346, painted on every intermodal freight container in the world. It's made up of a 3-letter owner code, a 1-letter equipment category identifier (almost always 'U' for freight containers), a 6-digit serial number, and a single check digit used to catch transcription errors during handoffs between ships, ports, rail, and trucks.
The validator strips whitespace, verifies the 11-character format, maps each of the first 10 characters to its ISO 6346 numeric value (digits as themselves; letters follow a table that skips every multiple of 11 — so B jumps from 10 to 12, L from 21 to 23, and V from 32 to 34), multiplies each by an increasing power of 2 (weights 1, 2, 4, 8, 16, 32, 64, 128, 256, 512), sums the results, and takes the sum modulo 11 as the check digit. If that remainder is 10, the combination has no valid check digit and is never actually issued.
Use this to verify a container number read off a bill of lading, port terminal system, or the container itself before using it in a tracking or customs system, to debug why a container number is being rejected by a validation layer, or to sanity-check a number that may have been transcribed incorrectly.
Instant, fully client-side validation with no data ever leaving your browser. Note this checks structural validity only — it does not confirm the container is currently registered to a real shipping line, which requires a lookup against the Bureau International des Containers registry.
Key Features
- Full 11-character ISO 6346 format validation
- Decodes owner code, equipment category, and serial number
- Recomputes and compares the official mod-11 check digit
- Flags the rare remainder-10 case where no valid check digit exists
- Verified against the standard published ISO 6346 worked example
- 100% browser-based, no data ever transmitted
FAQ
Container Number Validator — Frequently Asked Questions
What is a shipping container number?
It's an 11-character code, standardized as ISO 6346, painted on every intermodal freight container. It identifies the owning company, the equipment type, and a unique serial number, and is used throughout the shipping industry for tracking, customs, and billing.
What does the 4th letter in a container number mean?
It's the equipment category identifier. 'U' is used for all standard freight containers, 'J' for detachable freight container-related equipment, and 'Z' for trailers and chassis. The overwhelming majority of containers you'll encounter use 'U'.
How is the container number check digit calculated?
Map each of the first 10 characters to a numeric value — digits keep their value, letters use a special ISO 6346 table that skips every multiple of 11. Multiply each value by an increasing power of 2 (1, 2, 4, 8, 16, 32, 64, 128, 256, 512), sum the results, and take the total modulo 11. That remainder is the check digit — unless it's 10, in which case no valid check digit exists for that combination.
Why does my container number fail validation?
The most common cause is a single mistyped or transposed character, especially when reading a number off a container in the field where paint can be worn or hard to read. Also confirm the code is exactly 11 characters with no spaces.
Does a valid check digit mean the container is real?
No. This validator only confirms the code is structurally well-formed. It does not confirm the container is currently registered to a real shipping line or actively in service, which would require a lookup against the Bureau International des Containers (BIC) registry.
Tips
- Container numbers are usually stenciled in large characters on the container's doors and side — read carefully, as worn paint can make similar-looking characters (0/O, 1/I) hard to distinguish
- The first 3 letters are the owner code, registered with the BIC; the 4th letter is almost always 'U' for freight containers
- If the check digit fails, try re-reading the number from the container — the most common error is a single transposed character
- This validator never sends your container number anywhere — the check digit is recomputed entirely in your browser
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