Every product barcode — from a pack of gum to a shipping container — includes a check digit calculated using the GS1 standard algorithm. This single digit catches scanning errors and typos that could send the wrong product to a customer or throw off inventory counts. The GTIN Check Digit Calculator lets you validate existing barcodes or generate the correct check digit for new product numbers, across all major formats including UPC-A (12 digits), EAN-13, GTIN-8, and GTIN-14.
How to Use the GTIN Calculator
The calculator works in two modes:
Validate: Enter a full GTIN (with check digit) to verify it's correct. The tool auto-detects whether it's GTIN-8, 12, 13, or 14 and runs the GS1 check digit algorithm.
Generate: Enter a GTIN missing its last digit, and the tool computes the correct check digit. This is useful when creating new product codes or verifying label printing.
The step-by-step visualization shows:
- Each digit paired with its weight (alternating 1 and 3, right to left)
- The product of each digit × weight
- The sum of all products
- The check digit = (10 - (sum mod 10)) mod 10
GTIN Format Guide
GS1 defines four standard GTIN lengths:
- GTIN-8 (EAN-8): 8 digits. Used for small packages where a full barcode won't fit (e.g., chewing gum packs).
- GTIN-12 (UPC-A): 12 digits. The standard barcode on products sold in the US and Canada.
- GTIN-13 (EAN-13 / ISBN-13): 13 digits. The international standard used in Europe, Asia, and for books (ISBN-13).
- GTIN-14 (ITF-14): 14 digits. Used on shipping containers and cases of products, not individual retail items.
All four formats use the exact same check digit algorithm — only the number of digits changes.
The GS1 Check Digit Algorithm
The algorithm is straightforward:
- Starting from the rightmost position (not counting the check digit), assign alternating weights of 1 and 3, moving left.
- Multiply each digit by its weight.
- Sum all the products.
- Check digit = (10 − (sum mod 10)) mod 10.
Example for UPC-A 03600029145X:
- Weights: 1,3,1,3,1,3,1,3,1,3,1
- Products: 0,9,6,0,0,0,2,27,1,12,5 = sum 62
- Check digit = (10 − (62 mod 10)) mod 10 = (10 − 2) = 8
Step-by-Step Instructions
- 1Enter a GTIN number (8, 12, 13, or 14 digits).
- 2The tool auto-detects the format (GTIN-8, UPC-A, EAN-13, or GTIN-14).
- 3In Validate mode: see if the check digit is correct.
- 4In Generate mode: enter all digits except the last to compute the check digit.
- 5View the step-by-step calculation showing weights, products, and the final sum.