Few line items in a product launch budget look as trivial as a barcode. A pack of numbers costs less than a single sample shipment, and plenty of resellers will sell you a thousand of them for the price of lunch. Yet the identifier attached to a product is the key that every marketplace, search engine, retailer and warehouse uses to decide what that product is, who owns it and which listing it belongs to. Get the GTIN UPC for Amazon listings wrong and the problems show up months later as blocked uploads, merged listings, suppressed offers or a buy box shared with a stranger.
This guide explains what each identifier actually identifies, where legitimate codes come from, how to assign them across variants and bundles, when an exemption makes sense, and how to unwind a listing that is attached to the wrong number. It is written for sellers on Amazon first, but the same logic applies on Walmart, Google Shopping, eBay and wholesale channels, because they all read the same global standard.
In short
- A GTIN identifies a trade item, not a brand or a listing. UPC (12 digits) and EAN (13 digits) are two formats of the same GS1 system; an MPN is the manufacturer’s own part number and is not globally unique.
- Buy codes from GS1 (directly, or a single GTIN from GS1 US) if you are the brand owner. Amazon says it verifies product IDs against the GS1 database, and resold codes often trace back to another company’s prefix.
- Every distinct sellable variant needs its own GTIN: each size, color, pack count and bundle. Reusing a code across variants is the single most common catalog error.
- GTIN exemptions exist for private label, handmade, bundles and some generic goods, but they are granted per brand and category and work best when the brand is also enrolled in Brand Registry.
- Fixing a wrong GTIN rarely means editing a field. It usually means a catalog support case, a new code, and sometimes a fresh listing, so the cheapest fix is getting the code right before the first upload.
What GTIN, UPC, EAN and MPN each identify
GTIN stands for Global Trade Item Number. It is the umbrella term used by GS1, the not-for-profit standards body that manages the barcode system in more than 100 countries. A GTIN identifies one specific trade item: a product at a particular configuration that is priced, ordered or invoiced. A 500 ml bottle and a 1 liter bottle of the same shampoo are two trade items, and so are a single bottle and a case of twelve.
UPC and EAN are not competing standards. They are different lengths of the same numbering system. The UPC-A barcode common in North America encodes a 12-digit GTIN-12, while the EAN-13 barcode used in most other markets encodes a 13-digit GTIN-13. Modern scanners and marketplaces read both, and a GTIN-12 can be represented as a GTIN-13 by adding a leading zero.
That is why a US brand selling in Europe usually does not need a separate “EAN” for the same item.
The four formats you will meet
Beyond UPC and EAN, two more GTIN formats appear in retail catalogs. GTIN-14 is used for cases and cartons, typically printed as an ITF-14 barcode on shipping boxes. GTIN-8 is a compact code for very small packaging, issued sparingly. Books are a special case: an ISBN is a GTIN-13 in the 978 or 979 range, and marketplaces accept it in place of a UPC.
Where MPN, SKU and ASIN fit
An MPN (manufacturer part number) is the code a manufacturer gives its own product, such as a model number. It is useful for search and for matching spare parts, but it is not globally unique; two unrelated companies can both have a part called “A100”. A SKU is your internal stock-keeping code and is never shared with the outside world as an identifier. An ASIN is Amazon’s own catalog number, created when a product is first listed; a GTIN is the external key that Amazon uses to decide whether a new upload matches an existing ASIN.
| Identifier | Length | Who issues it | Globally unique | Typical use |
|---|---|---|---|---|
| GTIN-12 (UPC-A) | 12 digits | GS1 member organizations | Yes | Consumer units in North America |
| GTIN-13 (EAN-13) | 13 digits | GS1 member organizations | Yes | Consumer units outside North America, ISBNs |
| GTIN-14 (ITF-14) | 14 digits | Derived from the brand’s GS1 prefix | Yes | Cases, cartons and inner packs |
| GTIN-8 (EAN-8) | 8 digits | GS1 member organizations, on request | Yes | Very small packaging |
| MPN | Varies | The manufacturer | No | Model numbers, parts, search matching |
| SKU | Varies | The seller | No | Internal inventory and order systems |
| ASIN | 10 characters | Amazon | Within Amazon only | Amazon catalog pages |
The last digit of every GTIN is a check digit calculated from the others using a modulo 10 formula. Marketplaces reject codes that fail the check, which catches typos but not ownership problems. A number can be mathematically valid and still belong to someone else, which is the heart of most identifier trouble. For a broader view of how identifiers sit alongside titles, attributes and images, see our guide to product data and the digital shelf.
Buying barcodes from GS1 versus resellers
Every legitimate GTIN starts with a GS1 company prefix, a block of digits licensed to one company. The rest of the number is assigned by that company to its own items. When you buy a “barcode” from a reseller, you are really buying a number carved out of a prefix that was originally licensed to somebody else, often, according to GS1 US, a company that joined its predecessor, the Uniform Code Council, before 2002, when licensing terms changed, and later sold off unused numbers.
For years that distinction mattered little. It began to matter when large marketplaces started checking codes against GS1 data. Amazon’s seller documentation states that it verifies the authenticity of product UPCs using the GS1 database and that listings with UPCs that do not match the brand’s information may be removed. Walmart Marketplace and Google Merchant Center publish similar guidance favoring GS1-issued codes for branded products.
What GS1 US charges
GS1 US sells two products for brand owners. The first is a single GTIN, aimed at sellers with one or a handful of products, with a one-time fee and no annual renewal. The second is a company prefix with a capacity of 10, 100, 1,000 or more numbers, which carries an initial fee plus an annual renewal. As of 2026, GS1 US lists the single GTIN at around $30 per number and the 10-number prefix at around $250 initially with a smaller yearly fee, but pricing tiers change, so verify the current schedule on the GS1 US website before budgeting.
Outside the US, each country’s GS1 member organization sets its own prices, usually tied to company revenue. A UK, German or Australian brand normally licenses through GS1 UK, GS1 Germany or GS1 Australia, and the resulting codes are valid worldwide.
Why resold codes cause problems
A reseller code is not illegal to buy, but it carries three structural risks. The prefix lookup in GS1’s Verified by GS1 service shows the original licensee, not you, so the brand name attached to your listing will not match the GS1 record. The same number may have been sold before, or used on a real product years ago, which means it might already be attached to an ASIN for something unrelated. And if the original licensee let its membership lapse, the prefix may be flagged in GS1 data as inactive.
| Factor | GS1-issued code | Reseller code |
|---|---|---|
| Upfront cost | Higher (single GTIN or prefix fee) | Very low, often cents per code |
| Ongoing cost | Annual fee for prefixes; none for single GTINs | None |
| Brand shown in GS1 lookup | Your company | The original prefix licensee |
| Amazon verification | Matches brand data | Frequently fails or triggers review |
| Accepted by big-box retailers | Yes, usually required | Usually rejected in vendor onboarding |
| Risk of prior use | None, numbers are new | Unknown, cannot be checked fully |
| Ability to create case codes (GTIN-14) | Yes, from your own prefix | Not reliably |
The math usually favors GS1 for any brand that plans to stay in business. A reseller code saves a few hundred dollars once; a blocked listing during a launch can cost a full season of sales, plus the time spent in support queues.
Assigning identifiers across variants and bundles
The GS1 allocation rules come down to one principle: if a buyer or a supply chain partner needs to tell two items apart, they need different GTINs. That covers far more than most first-time sellers expect.
Variants
Each combination of size, color, flavor, scent, material or capacity that a customer can select needs its own GTIN. A T-shirt sold in five sizes and four colors is 20 trade items and 20 codes. On Amazon these become 20 child ASINs under one parent; the parent itself does not carry a GTIN because it is not a sellable item. The same logic applies to Shopify variants, Walmart variant groups and Google Shopping item groups.
GS1 guidance also calls for a new GTIN when a change is material to the buyer: a change in net content, a new declared size, a change to the brand name, or a significant formula change that a shopper would notice. Cosmetic packaging refreshes that leave the product and quantity unchanged generally keep the same code. Check the GS1 GTIN Management Standard for the full decision tree, because edge cases such as seasonal packaging and promotional bonus packs are spelled out there.
Multipacks and bundles
A pack of three of the same item is a different trade item from a single unit, so it needs its own GTIN. A bundle that combines different products (a razor, blades and shaving gel sold together) is also a new trade item. The brand that assembles the bundle is responsible for assigning it a code from its own prefix, or for using a bundle exemption where the marketplace allows one.
A common mistake is listing a bundle using the GTIN of its main component. On Amazon that attaches the bundle to the single-item ASIN, mixing bundle offers with single-unit offers and generating “not as described” complaints. Amazon’s own bundling policy requires bundles to have a unique identifier distinct from any component.
A simple allocation routine
- Build a master sheet with one row per sellable item before buying any codes, so you know how many you need.
- Assign numbers sequentially from your prefix, and never reuse a GTIN that has been on a product sold to the public, even after the item is discontinued. GS1 guidance for most consumer goods discourages reuse entirely.
- Register each item in GS1’s product data tool (GS1 US calls it Data Hub) with brand, description, size and image, so verification services see a complete record.
- Generate the barcode artwork from the number, not the other way around, and check print quality before a production run.
- Store the GTIN as text, not as a number, in every spreadsheet and system, so leading zeros survive.
That last step sounds pedantic, but stripped leading zeros are a constant source of failed uploads. Spreadsheet software that converts 012345678905 into 12345678905 has broken more feeds than any marketplace policy.
GTIN exemptions: who qualifies and how to apply
Marketplaces recognize that not every product has a GTIN. Amazon offers a GTIN exemption that lets a seller list products without a UPC or EAN in specific categories and for specific brands. It is designed for cases where a product genuinely has no barcode, not as a shortcut for avoiding the GS1 fee.
Typical qualifying situations
- Private label or own-brand products where the brand owner has not issued barcodes and sells only through its own channels.
- Handmade goods, including items sold through Amazon Handmade, where each piece is unique or made in small batches.
- Bundles assembled by the seller, in categories where Amazon permits bundle exemptions.
- Generic or unbranded products, typically listed with the brand field set to “Generic”, in categories that allow it.
- Certain parts, accessories and specialty items where the manufacturer does not barcode its products.
Amazon’s process runs through Seller Central: the seller selects the category and brand, then submits product images that show the packaging from all sides and demonstrate the absence of a barcode. Approval is granted for a brand and category combination rather than for a single listing. Requirements and eligible categories change, so read the current Seller Central help page on GTIN exemptions before applying.
Exemptions and Brand Registry
An exemption on its own does not protect the listing. Without a GTIN, the main thing tying an ASIN to your brand is the brand field and Brand Registry status. Brands enrolled in Amazon Brand Registry gain more control over listing content and can create listings using a GTIN exemption tied to their registered trademark. That combination is the closest thing to a clean ownership record for products without barcodes.
The tradeoff is portability. A product listed on an exemption can be harder to sell through other channels later. Google Shopping accepts products without GTINs if you set the identifier_exists attribute correctly, but performance is often weaker without one, and most brick-and-mortar retailers will not onboard an item without a GS1 code. Brands that expect wholesale distribution usually buy codes early rather than unwind an exemption later.
What happens when two sellers claim the same code
Duplicate GTINs surface in several ways. A new upload fails with a message that the product ID is already associated with a different product. A listing goes live and immediately merges into an existing ASIN with the wrong title and images. Or, more quietly, a stranger’s offer appears on your listing because their catalog file used your number.
The usual causes
The most common cause is reseller codes that were sold more than once. The second most common is internal: a brand reuses a code across variants, or a contractor copies the wrong cell in a feed. The third is deliberate: a seller lists a lookalike product using a popular brand’s GTIN to ride its listing. Amazon treats the last case as a policy violation and can remove the offer, but the brand usually has to surface it first through a report or a Brand Registry tool.
How marketplaces resolve the conflict
Amazon’s catalog generally resolves conflicts in favor of the GS1 record and the brand owner’s data. If your code is genuinely yours, a Seller Central case with the GS1 certificate, a Verified by GS1 lookup screenshot and photos of the barcode on the packaging is usually enough to have the record corrected. If your code is a reseller number that also appears elsewhere, the realistic outcome is that you need a new code and the conflicting ASIN stays with whoever has the stronger claim.
Walmart runs a similar process through Seller Center, where an item conflict triggers a review and the seller is asked to provide proof of GTIN ownership. Google Merchant Center flags mismatches as “incorrect product identifiers” and may limit the item until the GTIN matches the brand. On all three platforms, ownership documentation from GS1 is the evidence that ends the dispute fastest. Brands dealing with outright counterfeits on top of identifier conflicts should treat it as a broader brand protection issue; our piece on handling a counterfeit listing crisis on marketplaces covers the escalation path.
Fixing a listing attached to the wrong identifier
On most marketplaces the product ID field on a live listing is effectively locked. Changing it is treated as creating a different product, because the GTIN is the matching key. That is why a wrong identifier rarely gets fixed by editing a field and saving.
Diagnose before you open a case
- Run the GTIN through Verified by GS1 and record which company and product the number is registered to.
- Search the marketplace catalog for the number to see every ASIN or item it is attached to.
- Compare the listing’s current title, images and attributes with your product data to see whether the listing merged into another record.
- Check your own feed history to confirm whether the error came from your side, such as a stripped leading zero or a copied cell.
Three repair paths
If the number is yours and correct, but the listing shows another company’s data, open a catalog support case with ownership proof and ask for the data to be corrected or the ASINs separated. If the number is yours but was assigned to the wrong variant, the cleanest route is often to close the incorrect offer, correct the mapping in your own system, and list the affected variants again with the right codes. If the number is not yours, stop using it, license a proper code, and create a new listing; trying to keep a contested number almost never works.
Reviews and ranking history are the painful part. Reviews stay with the ASIN, so moving to a new ASIN can reset social proof, and sales velocity, which feeds into how Amazon ranks products in 2026, restarts from zero. Amazon will sometimes merge a duplicate into the original ASIN when both describe the same product, so ask about a merge before accepting a fresh start.
Inventory and fulfillment side effects
Identifier fixes also touch the warehouse. FBA inventory is labeled with an FNSKU tied to a specific ASIN, so stock sitting under a wrong or closed ASIN must be relabeled, removed or recreated under the new listing. Merchant-fulfilled sellers have more flexibility because they control their own labels. That difference is one of the practical factors in choosing between FBA and FBM for products with a messy catalog history.
| Problem | Likely cause | Typical fix | Reviews kept? |
|---|---|---|---|
| Upload rejected: ID already in use | Reseller code or reused number | New GS1 code, new listing | Not applicable |
| Listing merged into wrong ASIN | Code shared with another product | Catalog case with GS1 proof, or new code | Depends on outcome |
| Variant shows wrong size or color | Codes swapped in feed | Correct mapping, relist affected children | Usually yes at parent level |
| Brand name mismatch warning | GS1 record shows another company | Use own prefix, update GS1 data | Yes if ASIN survives |
| Stranger’s offer on your listing | Third party using your GTIN | Report via Brand Registry tools | Yes |
Keeping identifiers consistent across channels
Identifiers are only useful if they are the same everywhere. A product carrying one GTIN on Amazon, a different one on Walmart and a third in your Shopify feed confuses price comparison engines, splits review syndication and makes wholesale onboarding slower. The goal is one source of truth for every item, with each channel reading from it.
For most growing brands that source is a product information management system, or at minimum a well-governed master spreadsheet, that holds GTIN, MPN, brand, dimensions and attributes for every sellable item. Channel feeds should be generated from that record rather than typed by hand. The same discipline applies to the attributes that sit next to the GTIN in a feed, which our guide to product feed optimization covers in detail.
Channel requirements at a glance
Amazon uses the GTIN to match offers to ASINs and verifies it against GS1 data. Walmart requires a GTIN for most items and checks it against GS1 during item setup.
Google Merchant Center asks for the GTIN on any product that has one and uses it to group offers and power comparison features. eBay requires product identifiers for branded new items in many categories and lets sellers mark “Does not apply” where no code exists. Wholesale buyers and EDI partners expect GTIN-12 or GTIN-13 on consumer units and GTIN-14 on cases.
International selling
Because GS1 codes are global, a single GTIN works across Amazon’s US, UK and EU stores and on marketplaces from Mercado Libre to Kaufland. There is no need to license separate EANs for each country, and doing so creates duplicate records that complicate cross-border catalogs. The exceptions are regulated categories with their own national product codes, such as some pharmaceuticals, where local rules apply. Sellers expanding abroad will find the wider marketplace picture in our complete guide to selling on global e-commerce marketplaces.
An identifier audit you can run quarterly
- Export every active listing from each channel with its GTIN and SKU.
- Join the exports against your master record and flag any SKU with more than one GTIN, or any GTIN on more than one SKU.
- Run a sample of codes through Verified by GS1 to confirm the brand and product data are current.
- Check that discontinued items are retired, not quietly recycled onto new products.
- Review marketplace health dashboards for identifier warnings and resolve them before they turn into suppressions.
Identifiers are the foundation that every other piece of catalog quality rests on. Titles, images and attributes only reach the right shoppers if the product is matched to the right record in the first place, which is why the identifier layer comes first in our broader product data and digital shelf playbook. A clean GS1 prefix, one code per sellable item and a single master record cost far less than one week of a blocked listing.
FAQ on product identifiers
Do I need a UPC to sell on Amazon?
For most branded products, Amazon requires a product ID such as a UPC, EAN, ISBN or JAN when creating a new listing. Sellers whose products genuinely have no barcode can apply for a GTIN exemption for specific brands and categories through Seller Central. Requirements vary by category, so check the current Seller Central guidance.
Is a UPC the same as a GTIN?
A UPC is one format of GTIN. The 12-digit number encoded in a UPC-A barcode is a GTIN-12. EAN codes are GTIN-13s from the same GS1 system, and both are accepted by Amazon and most other marketplaces worldwide.
Can I use cheap barcodes from a reseller?
You can buy them, but they carry risk. Resold numbers come from prefixes licensed to other companies, so GS1 lookups show someone else’s brand. Amazon says it checks product IDs against GS1 data, and listings that fail verification may be blocked or removed.
Do I need an EAN to sell in Europe if I have a UPC?
Generally no. A GTIN-12 from a UPC can be read as a GTIN-13 by adding a leading zero, and European marketplaces and retailers accept GS1 codes issued in any country. Buying separate EANs for the same item creates duplicate records.
Does each size and color need its own barcode?
Yes. Under GS1 allocation rules every distinct sellable variant is a separate trade item and needs its own GTIN. The parent listing that groups variants on Amazon does not carry a GTIN because it is not sold on its own.
What GTIN does a bundle use?
A bundle is a new trade item and needs its own unique identifier, not the GTIN of any component. Amazon’s bundling policy requires this. Some categories allow sellers to list bundles under a GTIN exemption instead.
Can I change the UPC on a live Amazon listing?
Not directly in most cases. The product ID is the key that matches your offer to an ASIN, so changing it usually means a catalog support case or creating a new listing with the correct code. Ask about merging duplicate ASINs to preserve reviews.
How do I check who owns a barcode?
Use the Verified by GS1 lookup service, which shows the company licensed to the prefix and, where the brand has registered it, the product data attached to the number. If the result shows a different company than yours, the code was not issued to you.
Can I reuse a barcode from a discontinued product?
GS1 guidance for most consumer goods says a GTIN should not be reallocated to a different product, because old data persists in retailer and marketplace systems for years. Assign a new number from your prefix instead.