How GS1 Numbers Work
A GS1 number (a GTIN on a product, an SSCC on a shipment, a GLN for a location) is your GS1 Company Prefix, a reference you assign, and a check digit. The check digit is the last digit. It is worked out from all the others with the mod 10 method in section 7.9 of the GS1 General Specifications, so a scanner or an EDI system can catch a mistyped or misread number before it reaches an order.
| Number | Digits | Identifies | Built from |
|---|---|---|---|
| GTIN-12 (UPC-A) | 12 | Retail products in North America, printed as a UPC-A barcode. | Company prefix + item reference + check digit |
| GTIN-13 (EAN-13) | 13 | Retail products outside North America, printed as EAN-13. | Company prefix + item reference + check digit |
| GTIN-14 | 14 | Cases and inner packs, printed as ITF-14 or GS1-128. | Indicator digit + GTIN of the unit (without its check digit) + new check digit |
| GTIN-8 (EAN-8) | 8 | Small retail items with no room for a full barcode. | GS1-8 prefix + item reference + check digit (issued one by one by GS1) |
| SSCC-18 | 18 | One shipped carton or pallet, printed as GS1-128 with AI (00). | Extension digit + company prefix + serial reference + check digit |
| GLN | 13 | A company or location: ship-to, bill-to, a store or a dock. | Company prefix + location reference + check digit |
Where Bad Check Digits Come From
- Spreadsheets dropping leading zeros. Excel turns 036000291452 into 36000291452, which then reads as an 11-digit number missing its check digit. Format the column as text, or keep the GTIN-14 form.
- Building a case GTIN by hand. Adding a 1 in front of a UPC without recalculating the last digit gives an invalid GTIN-14. The UPC to GTIN-14 tab does it properly.
- Retyped numbers. A swapped pair of digits changes the check digit, so it is caught. That is the point of it.
In X12 EDI the same numbers travel in the PO1 and LIN segments (qualifiers UP for UPC, UK for GTIN-14, EN for EAN-13) and in MAN*GM for SSCCs on an 856. The EDI Inspector checks every one of them in a pasted file, the SSCC label generator builds carton numbers and labels, and the ITF-14 generator draws case barcodes. GS1 explains the method with a worked example on its how to calculate a check digit page.
GTINs, SSCCs and GLNs must be built from a GS1 Company Prefix licensed to your company by your local GS1 member organisation, such as GS1 US or GS1 UK. Our examples use 0614141, the prefix GS1 uses in its own documentation. OrderSync builds these tools independently of GS1.