IMO Number Validator
ValidatorValidate IMO ship identification numbers. Checks the 7-digit format and recomputes the official check digit. Runs entirely in your browser.
About this tool
About IMO Number Validator
An IMO Number is a permanent, unique 7-digit identifier assigned by the International Maritime Organization to seagoing merchant ships, staying with the vessel for its entire life regardless of name, flag, or ownership changes. It's typically written with an 'IMO' prefix (e.g. IMO 9074729), and the final digit is a check digit that guards against transcription errors.
The validator strips the optional 'IMO' prefix and whitespace, verifies the 7-digit format, multiplies each of the first 6 digits by decreasing weights (7, 6, 5, 4, 3, 2), sums the products, and compares the last digit of that sum against the 7th digit.
Use this to verify an IMO number read off a vessel registry, bill of lading, or port state control record before using it in a tracking or compliance system, to debug why an IMO 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 number is currently assigned to a real, registered vessel, which requires a lookup against the IMO's own ship and company database.
Key Features
- Accepts input with or without the 'IMO' prefix
- Full 7-digit format validation
- Recomputes and compares the official check digit
- Clear error messages for each failure mode
- Verified against a real, published IMO number
- 100% browser-based, no data ever transmitted
FAQ
IMO Number Validator — Frequently Asked Questions
What is an IMO number?
An IMO Number is a unique, permanent 7-digit identifier assigned by the International Maritime Organization to seagoing merchant ships over a certain size. Unlike a ship's name or call sign, the IMO number never changes for the life of the vessel, even if it's renamed, reflagged, or sold.
How is the IMO number check digit calculated?
Multiply the first 6 digits by 7, 6, 5, 4, 3, and 2 respectively, sum the products, and take the last digit of that sum — it must equal the 7th digit.
Do I need to include the 'IMO' prefix when validating?
No, this validator accepts the number with or without the 'IMO' prefix (e.g. both 'IMO 9074729' and '9074729' work). The prefix is a labeling convention, not part of the checksum calculation.
Why does my IMO number fail validation?
The most common cause is a single mistyped or transposed digit. Also confirm the number is exactly 7 digits — some sources include extra formatting or omit leading zeros that are actually part of the number.
Does a valid IMO number mean the ship is currently registered?
No. This validator only confirms the number is structurally well-formed and its check digit is correct. It does not confirm the number is currently assigned to an active, registered vessel, which would require a lookup against the IMO's own GISIS ship and company database.
Tips
- Include or omit the 'IMO' prefix — both forms are accepted
- If the check digit fails, try re-copying the number from its original source — the most common error is a single transposed digit
- The IMO number is permanent for a vessel's lifetime, unlike its name, flag, or call sign — useful for tracking a ship across ownership changes
- This validator never sends your IMO number anywhere — the check digit is recomputed entirely in your browser
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