FNSKU vs UPC vs Manufacturer Barcode

FNSKU vs UPC vs Manufacturer Barcode: Which Does Amazon Require?

If you sell on Amazon FBA, barcodes are one of the first operational decisions you need to get right. Use the wrong one and your unit gets received as the wrong product, refused at the fulfillment center, or stranded. Inbound defect fees are a separate matter: they apply to units in shipments that are misrouted, deleted, abandoned or incomplete. In 2026, with updated FBA prep requirements and Amazon no longer offering its own prep service, understanding the difference between FNSKU, UPC, and manufacturer barcodes is more important than ever.

This guide explains exactly what each barcode is, when Amazon requires each type, and how to avoid the most common and costly labeling mistakes.

What Is a UPC (Universal Product Code)?

A UPC is a 12-digit barcode standard used globally across retail. It is not Amazon-specific. Every physical product sold in stores like Walmart, Target, or Home Depot uses a UPC. When you list a product on Amazon, the platform uses the UPC (or EAN, ISBN, or JAN) to match your listing to an existing catalog entry or to create a new ASIN.

Key facts about UPCs:

• Issued by GS1, the global standards organization
• Each UPC is unique to a specific product (not a specific seller)
• Amazon uses UPCs to identify products in its catalog
• A single UPC can be shared across multiple sellers offering the same product
• A single GS1 US GTIN costs $30 with no annual renewal, and a GS1 Company Prefix starts at $250 plus $50 a year for 10 products

The critical limitation of a UPC for FBA sellers: it identifies the product, not the seller. Until March 31, 2026, two sellers sending the same product under manufacturer barcode tracking had their units pooled, which Amazon called commingled inventory. Amazon ended that practice, so pooling is no longer how FBA stores your units.

What Is an FNSKU (Fulfillment Network Stock Keeping Unit)?

An FNSKU is Amazon's own barcode that ties a specific product to a specific seller. It is generated automatically when you convert a listing to FBA and choose Amazon's labeling requirement. The FNSKU is the most important barcode for FBA sellers because it ensures your inventory is tracked separately from every other seller offering the same product.

Key facts about FNSKUs:

• Unique to your seller account and your specific ASIN
• Amazon uses the FNSKU to track which units belong to which seller
• Ties every unit in the fulfillment network back to your account
• Must be printed and affixed to every unit before shipping to FBA
• Format: Amazon issued FNSKUs are 10 characters and in practice start with X00, though Amazon does not publish the format as a rule
• Generated in Seller Central under Manage Inventory > Print Item Labels

When a customer orders your product, Amazon scans the FNSKU to pull your specific unit from the shelf. This means if there is a quality complaint or return, Amazon can trace it directly back to your inventory, not someone else's.

What Is a Manufacturer Barcode?

A manufacturer barcode is the barcode that comes pre-printed on the product packaging from the manufacturer or brand owner. In most cases this is a UPC, EAN, JAN, or ISBN, the four manufacturer barcodes Amazon accepts. When Amazon refers to "manufacturer barcode" in its settings, it means the barcode already on the product that you can use instead of printing and applying an FNSKU.

Amazon ended stickerless commingled inventory on March 31, 2026. Brand Representatives can still identify units by the manufacturer barcode, but through FBA virtual tracking, with every unit assigned to their own account.

Key facts about manufacturer barcodes:

• Already printed on the product by the manufacturer
• Skipping FNSKU labels is only an option for Brand Representatives enrolled in Brand Registry
• Units are tracked to your own account through FBA virtual tracking, not pooled with other sellers
• Never an option for used, media, restricted, dangerous, consumable or topical products
• Not all product categories allow manufacturer barcode tracking

Key Differences: FNSKU vs UPC vs Manufacturer Barcode

When to Use Each Barcode Type

Use FNSKU when:

• You sell private label products
• You sell bundles or multipacks
• You want to protect your brand from counterfeit complaints
• You sell in categories prone to quality issues (supplements, beauty, food)
• You want full traceability and accountability for your inventory
• You are a new seller building your reputation

Use the manufacturer barcode only when:

• You hold the Brand Representative role for that product in Brand Registry
• The product is not used, media, restricted, dangerous, consumable or topical
• The package carries a scannable UPC, EAN, JAN or ISBN that matches the listing
• You want to save the labeling step at high volume

Important: since March 31, 2026 every seller who is not a Brand Representative for the product labels with FNSKU, and most experienced sellers and prep services use it on all FBA shipments anyway. The cost of printing and applying an FNSKU label is minimal compared to the risk of a refused shipment or an authenticity complaint.

The Commingled Inventory Risk: Why It Matters

Until March 31, 2026, commingled inventory meant Amazon stored your units alongside identical units from other sellers and shipped whichever was closest. Amazon has since ended the practice. While it lasted, the risks were:

• Counterfeit complaints: If another seller sends fake or low-quality units and a customer receives one on your order, you get the complaint, the return, and potentially an IP violation
• Negative reviews: Product quality complaints that are not your fault appear on your seller profile
• Account suspension: Repeated authenticity complaints can trigger Amazon's automated enforcement, which can suspend your listing or your entire account
• Loss of Buy Box: Quality metrics impact your eligibility for the Buy Box

2026 Policy Changes That Affect Barcode Requirements

Several changes in 2026 make FNSKU labeling even more critical:

• Amazon ended commingling on March 31, 2026: unless you are a Brand Representative for the product, every unit you send to FBA now needs an FNSKU label
• Amazon ended its FBA Prep Service: As of January 2026, Amazon no longer labels or preps products for sellers. You must apply FNSKUs yourself or use a third-party FBA labeling service
• Inbound defect fees: $0.32 to $5.72 per unit for shipments created on or after January 15, 2026, charged on misrouted, deleted or abandoned units and on incomplete shipments whose quantities differ significantly from the plan. A unit that arrives without the Amazon barcode it needs is not refused for that: Amazon marks it as defective, applies a barcode sticker itself and reports the defect on your Inbound Performance Dashboard, and a shipment created since January 1, 2026 without the required prep or label loses reimbursement for units that are damaged or cannot be traced
• Stricter scan verification: Amazon fulfillment centers now reject shipments at higher rates when barcodes are unreadable, misaligned, or do not match the shipment manifest
• Virtual bundles require FNSKU: All virtual bundle components must be individually FNSKU-labeled; manufacturer barcode is not an option

FNSKU Label Requirements and Specifications

If you are applying FNSKU labels, Amazon has specific requirements:

• Label size: 1 to 2 inches tall by 2 to 3 inches wide, which is Amazon's published specification
• Barcode format: the item label Amazon generates is Code 128, and Amazon's published spec asks for a scannable barcode in black ink on non-reflective paper
• Must include the FNSKU in human readable numbers, the product title, and the condition (new or used)
• Must cover any existing barcodes on the product to prevent scanning errors
• Labels must be scannable (no smudges, wrinkles, or low-contrast printing)
• Amazon's label tools are optimized for thermal printers, laser printers also work, and inkjet printers are not allowed. Print at 300 DPI or greater. Amazon's own fulfillment centers print on direct thermal Zebra printers

How PrepVia Handles FBA Labeling

At PrepVia's FBA labeling service, barcode accuracy is not a best-effort metric. It is a 99.9% accuracy guarantee backed by automated verification systems.

Here is how the process works:

• FNSKU generation and verification: We pull your FNSKU data directly from your Seller Central account to eliminate manual entry errors
• Thermal label printing: Industrial-grade thermal printers produce labels that are always scannable and smudge-resistant
• Old barcode coverage: Every existing barcode on the product is covered with your FNSKU to prevent misscans at Amazon facilities
• Scan verification: Every labeled unit is scanned before packing to confirm the correct FNSKU matches the correct product
• Turnaround: Standard 24-36 hour processing, or 35-hour FastLane for time-critical shipments

Whether you send 50 units or 40,000 units in a single shipment, every single product is FNSKU-verified before it leaves our facility. No mislabeled units. No scanning errors. No refused shipments.