What the thirteen digits mean
The number splits into three parts. The GS1 company prefix identifies you and runs from seven to ten digits depending on how many products you registered for. The item reference fills the space that leaves. The last digit is a check digit, computed rather than chosen.
The first two or three digits of the prefix are commonly read as a country code, and that is a persistent misunderstanding: they identify the GS1 member organisation that issued the prefix, not where the product was made. A UK company can perfectly legitimately sell goods manufactured anywhere carrying a 50x prefix.
How the check digit is calculated
Take the first twelve digits and multiply each alternately by 1 and 3, starting with 1 at the leftmost position. Sum the results, then the check digit is whatever value brings that sum up to the next multiple of ten — equivalently, (10 − sum mod 10) mod 10.
That single digit is what lets a scanner reject a misread rather than silently return the wrong product. It is also why pasting all thirteen digits here either validates or fails: if the final digit does not match the calculation, something upstream is wrong and printing it would produce a barcode that scanners refuse.
You need a GS1 prefix before you print
GS1 is the body that allocates prefixes, through national member organisations, for a joining fee and an annual renewal. Retailers verify that a barcode resolves to the brand that claims it, and the major grocers and marketplaces check this at onboarding.
Resold or 'lifetime' barcode numbers bought from third-party sellers are a recurring trap. They are usually blocks issued before GS1 tightened its licensing, and while they scan perfectly, they are registered to another company — which surfaces as a rejected listing at exactly the wrong moment. If the product is going to a retailer, buy the prefix directly.
Print size and the quiet zone
The nominal EAN-13 symbol is about 37.29 mm wide by 25.93 mm high at 100% magnification, and the standard permits scaling between 80% and 200%. Going below 80% is the usual cause of a code that scans in the design studio and fails at a busy checkout.
The quiet zones are part of the symbol, not the margin around it: eleven modules on the left and seven on the right, which is why the '>' marker often appears at the right edge of packaging artwork. Do not let a design put text or a fold there. Keep bars dark on a light background, avoid red for the bars — many older scanners read with red light and will see nothing — and never rotate a linear barcode into a gradient.