Barcode Number Checker
Instantly verify the mathematical validity of any UPC, EAN, GTIN, or ISBN number. Our tool calculates the check digit locally in your browser.
Spaces and hyphens are ignored. ISBN-10 may end in X.
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Enter a supported number to calculate and compare its check digit.
How Barcode Validation Works
Barcode validation is a mathematical process used to ensure that a barcode number has been recorded correctly. It is not a search for a product in a database; rather, it is a calculation based on the digits within the number itself.
Most standard barcode formats (like EAN-13 or UPC-A) use a Mod-10 algorithm. The final digit of the barcode is a "check digit" calculated from the preceding numbers. If the calculated digit doesn't match the one printed on the package, the number is definitely wrong.
Decoding vs. Validation
Decoding involves converting the visual bars of a barcode image into a number. Validation takes that number and checks if its internal structure is mathematically sound.
Validation vs. Lookup
Validation does not tell you if a product exists. It only confirms the number is valid. A valid number could still be "unassigned" or not registered to any specific product.
What Check Digits Can and Cannot Prove
Check digits are designed to catch common human errors, such as:
- Single digit errors: Entering a 5 instead of a 6.
- Transposition errors: Entering 12 instead of 21.
However, a valid check digit cannot prove authenticity. Counterfeiters can easily generate valid check digits for fake numbers. To verify a product's identity, you must use an official registry lookup.
Frequently Asked Questions
What is the Mod-10 algorithm?
It is the standard formula used by GS1 for UPC, EAN, and GTIN numbers. It involves multiplying digits by alternating weights (usually 3 and 1) and finding the difference to the next multiple of ten.
Why does my ISBN have an 'X'?
Older ISBN-10 numbers use a Mod-11 algorithm. In this system, the remainder can be 10. Since 10 is two digits, the character 'X' is used as a placeholder for 10.
Is a valid GTIN the same as a genuine product?
No. Validation only checks the math. A fake product can have a mathematically "valid" barcode number.