Do You Need GS1 Barcodes to Use a 3PL? SKU and Barcode Rules Explained

You don't usually need GS1 barcodes to use a 3PL. The warehouse needs every product to carry a unique, scannable barcode linked to your SKU. GS1 barcodes, which carry a GTIN, become necessary when you sell through retailers or marketplaces that require them, so the decision depends on your sales channels rather than the warehouse.

Barcodes are one of the most common reasons stock gets stuck at goods in. A brand signs with a fulfilment partner, sends its first delivery and then finds that products have no barcode, the wrong barcode or two variants sharing the same one. The question that follows is usually whether GS1 barcodes are required.

This guide explains the difference between a SKU, a GTIN and Amazon's FNSKU, when GS1 numbers are expected, what makes a barcode scan reliably and what to ask before you send stock. If your labels are already wrong, in-house barcoding and re-labelling services can fix them before stock goes on sale.

SKU, GTIN, FNSKU and SSCC: What Is the Difference?

A SKU is your own internal code for a product variant, while a GTIN is a globally unique product number licensed through GS1 and represented in a barcode. The two serve different purposes, and most brands need both to manage their inventory and distribution effectively.

A Stock Keeping Unit (SKU) is created by your business and used to identify individual products or variants within your internal systems and warehouse stock records. Each SKU helps distinguish between different sizes, colours or product configurations, allowing the warehouse to track inventory accurately.

A Global Trade Item Number (GTIN) is issued through GS1 and is commonly represented in an EAN-13 or UPC barcode. Unlike an internal SKU, a GTIN provides a standardised way to identify products across retailers, marketplaces and point-of-sale systems, making it particularly important for brands selling through multiple channels.

An Amazon Fulfilment Network Stock Keeping Unit (FNSKU) is an identifier assigned by Amazon to track inventory within its fulfilment centres. It helps Amazon associate individual units with the correct seller and manage stock throughout the fulfilment process.

For products distributed in larger quantities, case barcodes, such as ITF-14 or GS1-128, are based on GS1 standards and used to identify outer cases during retail distribution. These help warehouses and distribution centres manage products at case level rather than scanning every individual unit.

A Serial Shipping Container Code (SSCC) is another GS1-based identifier used to identify individual pallets or other logistics units. It supports the tracking and movement of shipments through the supply chain, particularly when goods are transported between warehouses, distribution centres and retailers.

A warehouse links your SKU to a scannable barcode so every unit can be identified during goods-in, picking and packing. This connection is essential for maintaining accurate stock records and reducing fulfilment errors. The barcode can carry a GTIN or, for brands selling exclusively through their own online store, an internal code.

Where Are GS1 Numbers Required?

The requirement usually comes from where you sell, not from the warehouse. GS1 UK's answers to common barcode questions state that GTINs are required by most retailers and online marketplaces in order to sell products, because a GTIN identifies a product anywhere in the world.

If you sell only through your own website and have no plans for retail or marketplaces, the pressure is lower. Many brands start that way and find the requirement arrives with the first wholesale or marketplace deal, so it is often cheaper to set GTINs up before packaging is printed.

What Does Amazon Require?

Amazon has two separate questions: how a product is listed, and how units are tracked if Amazon stores them. GS1 UK explains that every item sent to an Amazon fulfilment centre needs a barcode, either an Amazon barcode such as FNSKU or a GS1 barcode, while sellers posting products directly to buyers do not need one for that purpose.

Listing a new product normally needs a product ID. GS1 UK says it shares new member data with Amazon daily, so it can take up to 72 hours for new numbers to become valid on Amazon, and that GS1 UK's GTIN-13 numbers should be listed under the product ID type EAN. Where a brand has no GTIN, GS1 UK notes that Amazon can grant an exemption for private label, generic or handmade products and issue its own identifier, a GCID. If you plan to sell through retailers as well, an exemption does not replace GTINs.

For Seller Fulfilled Prime and other merchant-fulfilled orders, your own warehouse ships the parcel, so the 3PL scans your product barcode, not an FNSKU. Fulfil with Synergy's Amazon Seller Fulfilled Prime service works this way.

Why the Source of Your Barcodes Matters

Buy GTINs directly from GS1. GS1 UK states that the only place to get legitimate GTINs is directly from GS1, and that numbers obtained elsewhere will not be traceable to your brand and may not be unique.

Resold numbers can cause problems with trading partners later, including listings that do not match your brand. If you already use barcodes from a reseller, check they are accepted by every channel you plan to use before you scale, because changing barcodes means relabelling or reprinting stock.

Unit, Case and Pallet Barcodes

Retail and wholesale add more levels of labelling. GS1 UK explains that EAN and UPC barcodes are scanned at tills, while ITF-14 and GS1-128 barcodes are typically used on cases and shippers.

A product can therefore need a unit barcode for the shop, a case barcode for the distribution centre and a pallet label carrying an SSCC. Retailers set their own specifications, so ask for the labelling requirements before production, not after. Our guide to choosing a 3PL for retail compliance and wholesale orders explains what to check.

What Makes a Barcode Scan Reliably?

A barcode only helps if it scans first time at every point in the warehouse. Size, contrast and placement decide that.

GS1 UK gives the standard size of an EAN-13 barcode as 37.29mm wide by 22.85mm high, with a minimum magnification of 80%. Bars must be darker than the background with good contrast, and barcodes printed as pale lines on a dark background cannot be read. Place the barcode on a flat surface, away from seams and folds, and test a printed sample with a scanner before ordering a full run of packaging.

Are 2D Barcodes Replacing EAN Barcodes in 2027?

Not overnight. GS1 UK explains that 2027 is the date the retail industry expects to be able to scan QR codes powered by GS1 at the till, not the date EAN and UPC barcodes disappear, and that both will appear on packs during a transition.

For a brand using a 3PL, the practical step is to keep a linear barcode on every unit and confirm with your warehouse that any new 2D codes do not confuse scanning at goods in or packing.

Common Barcode Problems

The same problems recur across brands. Products arrive with no barcode at all. Variants share one barcode, so a size 10 is picked for a size 8. A barcode is printed but will not scan. The barcode does not match the product record, so goods in cannot match the delivery to the ASN. Old and new packaging with different barcodes are both in stock.

Each creates exceptions, delays and counts that do not match, and errors that start at the barcode spread across every channel. Our article on why inventory accuracy drops across multiple sales channels shows how.

Questions to Ask a 3PL About Barcodes

Ask these before your first delivery:

• Which barcode formats can you scan, and what do you require at goods in?
• What happens when stock arrives with no barcode or the wrong one?
• Can you label or re-label stock in-house, and how is that quoted?
• How are barcodes linked to our SKUs in your system?
• Can you print case and pallet labels for retail orders?
• How do you keep old and new packaging versions apart?
• Who owns the conversation if a channel rejects a barcode?

Why Brands Choose Fulfil with Synergy for Labelling

Fulfil with Synergy, the Northampton-based third-party logistics provider, handles barcoding and re-labelling in-house as part of its value-added services, so labelling problems can be fixed in the same building where stock is received and held. Retail work includes in-house barcode and box-end label printing.

Its pre-retail preparation team works to retailer-specific unit, case and pallet labelling requirements, along with bespoke packing lists, RDD dates, bookings and transport. Fulfil with Synergy describes this team as highly tenured, which matters because retail labelling rules vary by customer. Small relabelling jobs are quoted from a packing list, a job specification and samples.

In the warehouse, the RedPrairie Dispatcher system tracks stock to unit, SKU, batch and location level, and AutoStore automation works with barcode verification to maintain pick accuracy. That is why clean barcode data matters before stock arrives. Dedicated account management helps you decide what to fix at the supplier and what to fix on arrival, whether you sell direct, on Amazon or through multi-channel and retail routes.

A Barcode Checklist

1. List every SKU and its barcode.
2. Check each variant has its own unique code.
3. Confirm the barcodes come from GS1 and are accepted by every channel you use.
4. Print and scan a sample of each.
5. Agree what labelling the warehouse will do and what must be done before shipping.
6. Ask retailers for case and pallet label rules.
7. Record barcode changes and the date they take effect.

Launching for the first time? Our guide to the fulfilment infrastructure a DTC brand needs in month one covers barcodes alongside packaging, carriers and returns.

FAQ

Do I need GS1 barcodes to use a 3PL?

Not always. A 3PL needs every product to carry a unique, scannable barcode linked to your SKU, but that barcode does not have to be a GS1 GTIN if you sell only through your own store. GS1 barcodes become necessary when you sell through retailers or marketplaces, because GS1 UK says most of them require GTINs. If you expect to add wholesale or marketplace channels, set up GTINs before you print packaging, so you do not have to relabel stock already in the warehouse.

Does Amazon require GS1 barcodes?

Amazon normally asks for a product ID such as an EAN when you list a new product, and GS1 UK says new GS1 numbers can take up to 72 hours to become valid on Amazon. Products without a GTIN may qualify for an exemption if they are private label, generic or handmade, in which case Amazon issues a GCID. Units stored in Amazon fulfilment centres need a barcode, either an FNSKU or a GS1 barcode. Seller Fulfilled Prime orders ship from your own warehouse, which scans your product barcode.

What is the difference between a SKU and a barcode?

A SKU is your own internal code for a product variant, chosen by you and meaningful only in your systems and your warehouse's. A barcode is the scannable symbol printed on the product, and it can carry either a GTIN, which identifies the product globally, or an internal code. Your warehouse links each SKU to a barcode so that every unit can be scanned at goods in, pick and pack. Problems start when two variants share a barcode or a barcode is not linked to the right SKU.

Can I buy barcodes from a reseller?

You can, but GS1 UK advises against it. It states that the only place to get legitimate GTINs is directly from GS1, and that numbers bought elsewhere will not be traceable back to your brand and may not be unique. That can cause problems with marketplaces and retailers that check numbers against GS1 data. If you already use reseller barcodes, confirm they are accepted by every channel you plan to sell through before you scale, because replacing them later means relabelling or reprinting stock.

Can Fulfil with Synergy label products that arrive without barcodes?

Yes. Fulfil with Synergy's value-added services include in-house barcoding and re-labelling, and retail work includes barcode and box-end label printing to retailer-specific unit, case and pallet requirements. Small jobs are quoted from a packing list, a job specification and samples. Because the work happens in the same Northampton facility where stock is received, products can be corrected and put away without being sent elsewhere. Your account manager can help decide what is better fixed at the supplier for future deliveries.

If you are unsure whether your barcodes will work for your channels and your warehouse, talk to Fulfil with Synergy before you send stock.