Free VIN Validator & Format Checker

How the VIN Validation Algorithm Operates

Automotive VIN validation relies on strict syntactic and mathematical checks developed jointly by the Society of Automotive Engineers (SAE), the International Organization for Standardization (ISO), and the United States Department of Transportation. When you inspect a used vehicle, buying a car with an invalid VIN can indicate stolen vehicles, cloned titles, or fraudulent vehicle history reports.

Rule 1: Length and Alphanumeric Grammar

Every standardized VIN since 1981 contains exactly 17 characters without spaces or hyphens. Any input with 16 or 18 characters is immediately defective. Furthermore, only characters 0–9 and uppercase Roman letters are allowed, with three strict exceptions: the letters I, O, and Q. Because optical scanners and manual inspectors could easily confuse an "I" with a "1" or an "O"/"Q" with a "0", these three letters are never used in valid VINs.

Rule 2: Mathematical Checksum Algorithm (Modulo-11)

The 9th character in North American VINs is calculated using a weighted modulo-11 algorithm:

1. Transliteration: Each alphabetical character is converted into a predefined integer from 1 to 9 (for example, A=1, B=2, C=3, K=2, S=2). Numbers retain their literal values.
2. Weight Multiplication: Each of the 17 positions is assigned a weight: [8, 7, 6, 5, 4, 3, 2, 10, 0, 9, 8, 7, 6, 5, 4, 3, 2]. Position 9 has a weight of 0 because it is the check digit itself.
3. Summation: The products of each transliterated character value and position weight are added together.
4. Modulo 11: The total sum is divided by 11. The remainder dictates the check digit: a remainder from 0 to 9 results in that digit, while a remainder of 10 is denoted by uppercase Roman numeral X.