UPC/EAN Barcode Check Digit Validator

What is the UPC/EAN Check Digit Validator?

UPC-A (12 digits, common in the US/Canada) and EAN-13 (13 digits, common everywhere else) barcodes both end in a check digit — calculated from the other digits using a fixed GS1 formula — that lets scanners detect a misread or mistyped code. This tool validates an existing barcode's check digit, or calculates the correct one if you only have the product's data digits.

The formula

Starting from the digit immediately before the check digit and working left, digits alternate weights of 3 and 1 (the rightmost data digit is weighted 3). Multiply each digit by its weight, sum them, then the check digit is whatever number makes the total a multiple of 10: check = (10 − (sum mod 10)) mod 10. This is the same underlying rule for both UPC-A and EAN-13; the formats just differ in how many digits come before the check digit.

How to use it

1. Enter 11 digits (UPC-A without its check digit) or 12 digits (EAN-13 without its check digit) to calculate the missing check digit.
2. Enter 12 digits (full UPC-A) or 13 digits (full EAN-13) to validate an existing barcode.
3. Spaces and dashes are ignored, so you can paste a barcode exactly as printed.

This is useful when setting up new Amazon listings that require a UPC/EAN, checking a supplier-provided barcode for typos, or troubleshooting a barcode that a scanner keeps rejecting.