Check Digit Calculator
Calculate and verify check digits for EAN-13, UPC-A, and ISBN-13 barcodes.
Check Digit Calculator
What is a Check Digit?
A check digit is the last digit of a barcode number, calculated from the preceding digits using a specific algorithm. It is used to verify that the barcode has been scanned or entered correctly. If any digit is wrong, the check digit calculation will fail, alerting the system to an error.
How Check Digits Work
For EAN-13 and ISBN-13, the check digit is calculated by alternating weights of 1 and 3 across the first 12 digits, summing the weighted values, and taking the result modulo 10. The check digit is (10 - sum mod 10) mod 10.
For UPC-A, the algorithm uses alternating weights of 3 and 1 (reversed from EAN-13) across the first 11 digits.