SSCC & GLN Check Digit Calculator

One algorithm, several lengths

Every GS1 identification key ends in a mod-10 check digit computed the same way. Multiply each digit by an alternating weight of 3 and 1, add the products, and take whatever brings the total to the next multiple of ten.

The one thing that changes with length is where the weights land. The weighting is anchored on the right: the digit immediately left of the check digit always carries 3. On an even-length payload like a GLN’s 12 digits that means the leftmost digit carries 1, and on an odd-length payload like an SSCC’s 17 it carries 3. A calculator that anchors the weights on the left instead gets GTINs right and SSCCs wrong, which is exactly the kind of bug that survives casual testing.

SSCC and GTIN are not interchangeable

A GTIN identifies a kind of thing, so every identical jar of jam carries the same one. An SSCC identifies one specific logistics unit: this pallet, not pallets like it. That is why an SSCC must be unique and, per GS1, should not be reused for a long period after the unit it named has been broken down.