A SKU is a code you invent to identify your products inside your own operation; a GTIN is a global, unique number purchased from an official body that identifies that product to the entire world. Confusing the two is the error that stalls the most listings when a brand enters a marketplace for the first time.
The distinction matters because you control one and not the other. If your SKU is badly built, the problem is internal and you fix it in an afternoon. If you're missing the GTIN, you can't publish at all.
The five terms, in one table
| Term | What it is | Who assigns it |
|---|---|---|
| SKU | Internal code identifying each product variant in your inventory | You |
| GTIN | Global Trade Item Number; the product's universal identifier | GS1 (official body) |
| UPC | A 12-digit GTIN, the format used mainly in North America | GS1 |
| EAN | A 13-digit GTIN, the format used mainly in Europe | GS1 |
| Barcode | The graphic representation — the bars — of any of those numbers | Generated from the number |
The most common confusion: thinking "barcode" is a type of number. It isn't. It's the visual way of printing a number so a scanner can read it. UPC and EAN are both GTINs; only the digit count differs.
The SKU: what you control
Your SKU is your internal naming system. There are no official rules, but there are practices that save you pain later:
One SKU per variant, no exceptions. If you sell a t-shirt in three sizes and two colors, that's six SKUs, not one. Every combination a customer can order separately needs its own code. It's the rule most often broken and the one that causes the most inventory mismatches.
Readable but short. TEE-BLK-M tells you what it is at a glance; 8842 doesn't. But don't make it so long nobody can read it out over the phone.
No problematic characters. No spaces, slashes or accented characters. Many systems mangle them when importing or exporting files.
Never reuse a SKU. When you discontinue a product, that code dies with it. Recycling it merges the sales history of two different products and ruins any later analysis.
The GTIN: what you have to buy
GTINs come from GS1, the organization that administers the system worldwide. They assign you a company prefix, and from there you generate each product's number.
Two warnings that get expensive:
Don't buy "cheap" barcodes from resellers. There are sites selling loose GTINs well below GS1 prices. Those are codes originally assigned to another company and resold. Amazon and other marketplaces validate that the GTIN prefix matches the company publishing the listing, and when it doesn't, they block it. The savings turn into an entire catalog you can't upload.
If you manufacture your own brand, the GTINs are yours to get. If you resell another brand's product, that product already has its GTIN and you must use that one rather than creating a new one.
When the marketplace doesn't ask for a GTIN
There are exceptions. Some marketplaces allow listings without a GTIN in categories like handmade goods or registered private brands, usually through an exemption you request. It's a legitimate route, but don't assume it: it varies by category and platform, and changes over time. Verify it on the platform you're selling on before printing labels.
How this connects to your physical operation
This is where theory turns into real cost. When your product reaches a warehouse, someone has to identify it without opening the box or asking anyone.
- Product with no scannable barcode = someone identifies it by eye. It's slower, and it's where picking errors are born.
- Product with an unreadable code (blurry print, curved surface, covered by another label) = same problem, with the added twist that it looks solved.
- Two different products sharing one code = guaranteed mismatch, and a hard one to trace.
If your product arrives without a scannable code, a logistics operator can label it at receiving, but that's extra work billed per unit. Shipping product already labeled from origin is almost always cheaper.
Frequently asked questions
Do I need a separate GTIN per size and color? Yes. Every variant sold separately needs its own GTIN, just as it needs its own SKU.
Can I use my SKU as a barcode? For internal warehouse use, yes — a barcode can be generated from your SKU. For listing on a marketplace that requires a GTIN, no: they're different things.
Do GTINs expire? The number doesn't expire, but GS1 membership renews periodically. If you stop renewing, your codes can lose validation backing.
What if my supplier won't give me the GTIN? Request it formally before buying volume. If it's private-label product made by a third party, you're the one who registers the GTIN.
Having a properly coded catalog isn't bureaucracy: it's the condition for your inventory to reconcile, for listings not to stall, and for whoever prepares your orders not to have to guess. If you're building your catalog for marketplaces and want the physical side solved from day one, get a fulfillment quote — or see how we handle marketplace prep.