This page assumes you already understand what these identifiers are and when you need one — see Understanding Product Identifiers for that, and How to Determine Whether a Product Already Exists for the broader catalog-matching decision. This page is just the mechanics: given one identifier, how do you actually find the other.
Going UPC → ASIN (you have a barcode, want the Amazon listing)
The free, reliable way: search for the product in Seller Central's "Add a Product" flow using the UPC/EAN directly, rather than a text search. If a matching catalog item exists, Amazon will surface it along with its ASIN. This is the same underlying catalog match Amazon itself uses to decide whether you're creating a new listing or can add an offer to an existing one (see Creating a New Listing vs. Adding an Offer), so it's also the most authoritative source — if Seller Central says no match, there genuinely isn't one in Amazon's catalog under that identifier.
If you don't have Seller Central access (checking a competitor's or supplier's product before deciding whether to source it, for example), you can search Amazon's retail site directly using the UPC in the search bar. This works inconsistently — Amazon's consumer-facing search isn't optimized for exact barcode matching the way the seller-side catalog search is — so a no-result here doesn't reliably mean no match exists, only that this particular search didn't find one.
Going ASIN → UPC (you have the Amazon listing, want the barcode)
Check the product detail page itself. Many Amazon listings display the UPC or EAN in the "Product information" or technical details section near the bottom of the page. This works for a meaningful share of listings, but not all of them — it depends on whether the brand submitted a GTIN at all (some categories don't require one) and whether the listing is private-label. A private-label product sold under Amazon's GTIN exemption generally won't have a public UPC to find this way, because it was never assigned one that Amazon displays — not because the information is being hidden.
If it's your own listing, your Seller Central inventory/catalog view shows the UPC you originally submitted when you created it — no searching required.
Third-party "ASIN to UPC converter" tools
A handful of seller-tool sites (SellerApp, Seller Assistant, Analyzer Tools, and others) offer free single-lookup converters. Worth knowing going in: none of the ones reviewed for this page disclose where their data actually comes from, and the limitation they all mention — that private-label items often can't be converted — is the same blind spot you'd expect from a tool reading the public product detail page rather than pulling from Amazon's own authorized catalog data. Treat a result from one of these as a convenience for a one-off check, not as an authoritative source for anything compliance-sensitive (confirming a GTIN registration dispute, for example) — cross-check against Seller Central directly if it matters.
The developer-grade way: Amazon's SP-API
Amazon's Selling Partner API has a Catalog Items endpoint that supports searching by identifier (including UPC/EAN) and returns matching ASINs programmatically. This is how software built for sellers — including some of the product-research platforms already covered on this site — likely does bulk or automated lookups under the hood. It's not a practical option for an occasional manual check: it requires registering as an SP-API developer and calling the endpoint against an authorized, connected Seller Central account, not an anonymous public lookup. If you're building or evaluating software that needs to do this at real volume, this is the legitimate path; if you just need to check one product, it's considerable overkill.
Common mistakes
- Assuming a private-label ASIN's missing UPC means the data is being hidden from you, rather than recognizing it likely was never assigned a public GTIN in the first place.
- Trusting a free converter tool's result for something compliance-sensitive (a GTIN ownership dispute, a brand-registry claim) without confirming against Seller Central's own catalog data directly.
- Confusing an MPN shown on the product page with a UPC — some listings display both, and they are not interchangeable (see Understanding Product Identifiers).
- Assuming the first ASIN a search returns is the right one for a multipack, bundle, or variation — the same base product can have several distinct ASINs depending on pack size or variant, each with its own UPC.