Quick verdict
Use SKUs to manage your internal inventory. Use UPCs to list products on Amazon, eBay, and every external platform. They work together — you'll have both assigned to every product in your catalog.
Side-by-side comparison
| Feature | UPC | SKU |
|---|---|---|
| Who made it | GS1 / UCC (standardized system) | You (your own format) |
| Who reads it | Everyone — universal | Only you (internal) |
| Format | 12-digit standard number | Whatever you want |
| Required by Amazon | Yes (to create a listing) | No (optional, you create it) |
| Printed on product | Yes, as a barcode | Usually internal only |
| One per product globally | Yes | No — can differ by seller |
What a SKU actually is
SKU stands for Stock Keeping Unit — it's an internal code you assign to a product to track it in your own system. You invent it. 'SHIRT-RED-L' is a valid SKU. So is '00492'. There's no standard format. Two different companies can have the same SKU meaning completely different products. It's shorthand for your warehouse, your spreadsheet, your Shopify backend.
What a UPC actually is
A UPC (Universal Product Code) is a 12-digit standardized number issued from a GS1 company prefix. It's registered globally — or at least traceable to a real company prefix. When a checkout scanner reads 012345678905, every system in the world resolves that to the same product. That's the point: universal, not internal.
Do they conflict with each other?
No. Most sellers use both: the UPC identifies the product to external systems (Amazon, eBay, retail scanners), and the SKU tracks it internally (Shopify inventory, your own spreadsheet, your 3PL warehouse). On Amazon Seller Central, when you create a listing you enter both — the GTIN (UPC) for the product, and optionally a Seller SKU for your own tracking. They coexist without issue.
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