What is a GTIN (Global Trade Item Number)? A guide for UK suppliers

A new retail customer's onboarding pack asks for a short list. The Transalis retail playbook sums it up: "Expect four things: a Global Location Number, a Supplier Number, barcodes that scan and, where asked, pallet labels." The barcodes are the visible part. The number inside each one is what the buyer's systems look up, and it names the product on the order and the invoice.

What is a GTIN?

GS1's identification key for a trade item. In GS1's words: "Global Trade Item Number (GTIN) can be used by a company to uniquely identify all of its trade items." A trade item is broader than a product on a shelf. "GS1 defines trade items as products or services that are priced, ordered or invoiced at any point in the supply chain."

The rule that follows is strict: "Each trade item that is different from another is allocated its own separate GTIN."

The GS1 General Specifications (Release 26.0, 2026) set the test: "A separate, unique GTIN is required whenever any of the trade item declarations are different in any way that is relevant to the trading process."

So where a single unit, a multipack and a case are each priced, ordered or invoiced, each one is a trade item with its own GTIN.

The GTIN names a line, not one physical unit. As the Transalis guide to SSCCs puts it, "A GTIN identifies a product line, and every unit of that line shares it." Locations take a different key: the GLN identifies a party or a location.

GTIN, EAN, UPC or barcode: what is the difference?

The GTIN is the number. The barcode is the carrier that holds it. GS1's specifications pair them for retail units: an "EAN-13 barcode (carrying a GTIN-13)" and a "UPC-A barcode (carrying a GTIN-12)".

Everyday usage blurs the two. Google Merchant Center's help page lists "EAN (in Europe / GTIN-13): 13-digit number", so an "EAN number" in everyday use is a GTIN-13.

• GTIN: the identification key itself, in one of four lengths.
• EAN-13: the barcode that carries a GTIN-13, the usual form on UK and European retail packs.
• UPC-A: the barcode that carries a GTIN-12, the North American form.
• ITF-14: a barcode for outer cases, covered below.

What are GTIN-8, GTIN-12, GTIN-13 and GTIN-14?

Four lengths of the same key. GS1 states that "GTINs are numeric strings that are available in four formats": GTIN-8, GTIN-12, GTIN-13 and GTIN-14.

A fixed-measure unit scanned at the till must use one of the first three. GS1 says such an item "SHALL be identified with a GTIN-8, GTIN-12, or GTIN-13."

GTINs shorter than 14 digits can also be written with leading zeros to fill 14 places. GS1 is clear that "The presence or lack of these leading zeroes does not change the GTIN data element value."

How are the digits of a GTIN built?

From three parts. Here they are for a GTIN-13.

1. The GS1 Company Prefix. "The GS1 Company Prefix is allocated by a GS1 Member Organisation to a system user." In GS1's words, "It makes the ID number unique worldwide but does not identify the origin of the item."
2. The item reference. "The item reference is assigned by the system user", meaning the company that holds the prefix.
3. The check digit. The last digit, worked out from the others. Its "verification, carried out automatically by the barcode reader, ensures that the number is correctly composed."

GS1 publishes the method. Working from the right, multiply the digits alternately by 3 and 1, starting with 3 on the digit next to the check digit. Then "Add results together to create sum", and "Subtract the sum from nearest equal or higher multiple of ten = Check Digit".

GS1's own worked example uses the first twelve digits 629104150021. The weighted sum is 57. The nearest multiple of ten at or above it is 60, and 60 minus 57 gives a check digit of 3. GS1 says the algorithm "is identical for all fixed length numeric GS1 data structures (including GDTI, GLN, GRAI, etc.) that require a check digit."

Who allocates a GTIN: brand owner, supplier or retailer?

For branded goods, the brand owner. GS1 gives the job to "the party that warrants the trade item declarations, known as the GTIN allocator", and states that "For branded items, the brand owner is the GTIN allocator".

For a UK supplier, that splits three ways:

• Your own brand: you allocate the GTIN, from your own prefix.
• An own-label line: the retailer does. GS1 names "The retailer: The retailer that sells the trade item under its own brand name."
• An importer or wholesaler: it allocates when it sells the item under its own brand name, or changes it "for example by modifying the packaging".

Timing is fixed too. "A trade item SHALL be assigned a GTIN before there is an offer made for sale of the trade item." Once a GTIN exists, a distributor, wholesaler or merchant further down the chain may not give the same unchanged item a different one.

How do you get GTINs in the UK?

Through a GS1 licence. GS1's rule is that "A GTIN allocator is licenced a GS1 Company Prefix and/or individual GS1 identification keys by a GS1 Member Organisation."

The Transalis guide to EDI numbers covers the UK route: "You register for a GLN through GS1 UK, which also issues the GS1 prefix used to generate GTINs for individual products." One registration covers your sites and your products. For prices and licence terms, go to GS1 UK.

Which GTIN goes on the outer case?

Its own, separate from the retail unit's. GS1 counts groupings as trade items: "This includes trade item groupings of retail and non-retail trade items that are also trade items". For a case of identical items, "The manufacturer or supplier has the option of either assigning a unique GTIN-13 or GTIN-12 to each trade item grouping or assigning a unique GTIN-14."

GS1 allows either, so check your customer's specification before you print.

A GTIN-14 is built from the unit's number:

• It starts with an indicator digit. "The indicator is a digit with a value of 1 to 8." GS1 adds that "The indicators have no meaning."
• Next comes the contained item's GTIN, less its check digit. For a GTIN-12 or GTIN-8 unit, GS1's table fills the spare places with leading zeros.
• A new check digit is then calculated.

On the case, "ITF-14 symbols can encode the GTIN-12, GTIN-13, or GTIN-14 of the item." A GS1-128 barcode can carry it instead, and GS1 says that choice is "particularly relevant" where the label also needs attribute information.

Ocado's supplier manual lists what its outer cases must show, including "Barcode (outer case NOT retail)". It warns that "if the outer cases are not clearly visually different, this may lead to cross-receiving and an invoice matching query."

The pallet takes a different code. GS1 notes that "The combination of a GTIN and a serial number (also known as SGTIN) does not replace the SSCC as the identifier of a logistic unit." The pallet code has its own guide: what is an SSCC.

When does a product need a new GTIN?

When the change matters to consumers, trading partners or the supply chain. GS1's GTIN Management Standard asks three questions: will consumers or trading partners be expected to tell the new version apart, is there a regulatory or liability disclosure, and is there a substantial impact on how the goods are shipped, stored or received? "At least one of the guiding principles must apply for a GTIN change to be required."

The rules suppliers meet most often:

• A new product. "Any new product requires the assignment of a new GTIN."
• Net content. "Any change (increase or decrease) to the legally-required declared net content that is printed on the pack, requires assignment of a new GTIN."
• Size or weight. "A change of over 20% to a physical dimension, on any axis, or gross weight, requires assignment of a new GTIN."
• Primary brand. "A change to the primary brand that appears on the trade item, requires assignment of a new GTIN."
• Case or pallet quantity. "A change to the number of trade items in a case or a change to the quantity of cases in a predefined pallet configuration, requires assignment of a new GTIN." A case that goes from 8 units to 12 needs a new case GTIN.
• Promotions. For a time-limited promotional pack, "No GTIN change is required at the retail consumer trade item/base unit level". That holds while the declared net content stays the same and size or gross weight moves by no more than 20%, as in GS1's own promotional example. An extra-free pack changes the declared net content, so it needs a new unit GTIN. The case and pallet still need their own.

A change at the retail unit carries upwards. The standard's change rules each add: "A unique GTIN is assigned at every existing level of the packaging hierarchy above the retail consumer trade item/base unit level." So when a pack drops from 500g to 450g, the unit, the case and any pallet with its own GTIN all get new numbers.

The standard also covers declared formulation, certification marks, predefined assortments and price on pack. Local law comes first: "All local legal and regulatory requirements supersede the GTIN Management Standard."

Drinks producers face one dated change. For packs in scope of the deposit return scheme from October 2027, Exchange for Change, which runs the scheme, says "All existing barcodes, including international barcodes, will need to be changed". The DRS guide for producers covers what that means.

When a new GTIN is assigned, GS1 says "it is essential that the brand owner provide the detailed information to trading partners about the item's characteristics." Ocado puts it in its own terms: "Any proposed changes to product details, including barcodes, case size and packaging, must be agreed with the relevant Buying Manager and the Supply Chain Team in advance of its arrival at a CFC".

Where does the GTIN sit in an EDI order and invoice?

On each product line, wherever the product has one. GS1's EANCOM standard is plain: "If Global Trade Item Numbers are available it is mandatory to use GTIN within the LIN segment." The same rule appears in the order and the invoice message. The Transalis guide to EDI numbers says it simply: "Product lines carry the GTIN for each item ordered."

On the order, "Where your products have GTINs, a retailer's order names each product by its GTIN, and your map has to turn that into your own product code." EDI mapping explained covers that translation. On the invoice, each billed line quotes the GTIN again; EDI invoice explained walks through the message.

The GTIN on an order line is the one for the unit being ordered, and that is often the outer case rather than the single pack. In GS1's own EANCOM order example, "The ordered item is a traded unit", and the message can state how many consumer units each traded unit holds. The Transalis guide to EDI numbers describes the GTIN as "An individual product, at the level it is bought and sold". So hold the GTIN of every pack level against the product, with the number of units each one contains, and invoice at the level ordered.

Your ERP has two details to get right. First, the same product can reach your systems as 13 digits or as 14 with a leading zero, for example from a scanned case label, and your system has to treat both as one item. GS1 allows either form in a database field, but "there SHALL be consistency within the database field about whether these leading zeroes are present or not." Second, the mapping only works if each product's GTIN is held against it in your ERP.

What goes wrong with GTINs when supplying a retailer?

Trouble starts when the barcode, the product record and the message disagree. The Transalis guide to EDI numbers describes the knock-on: "Orders can be rejected outright, sent to the wrong location, or matched to the wrong product line, which then holds up picking, despatch and invoicing."

Ocado's manual shows how one retailer handles it at goods-in. "Correct information must be detailed on the barcode. This must be SKU specific". It adds: "Incorrect barcodes may result in stock being sent to the non-conforming area and charges may be raised for storage of non-conforming stock." And it sets the habit that prevents it: "Barcodes should always be checked for scanning prior to a product's first arrival at Ocado and continually checked for quality and accuracy."

Four checks help:

1. Scan before you ship. The peak season checklist says it for new lines: "Do the same for the barcode on any new or repackaged line."
2. Check the case barcode carries the case GTIN, not the retail unit's.
3. Check every place the number lives: the pack, the ERP product record and the product data you send each retailer.
4. Tell partners before a change arrives.

For the full list of what a retailer expects at onboarding, see EDI requirements for retail suppliers.

Where Transalis fits

Transalis is a managed outcomes provider for B2B integration, EDI and eInvoicing. Transalis OpenEDI™ connects you to more than 15,000 live trading connections on a fixed-cost basis, with no per-transaction or VAN charges. Connect once, and reach every partner on the network.

Product data can travel the same way. With Product Catalogue Distribution, Transalis automates it: you share the catalogue once, and the platform converts and delivers it to each retail partner.

Transalis DataTrack™ gives you visibility into individual messages, so you can see where an identifier does not match and correct it before it causes a bigger problem further down the chain.

Start trading in days, or see the managed service on the EDI page. For how the GTIN sits beside your other identifiers, read what is an EDI number.