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SKU and Article Number
The SKU (Stock Keeping Unit) and the article number are the DNA of every fulfillment operation. They uniquely identify which product in which variant is stored, picked, packed, and shipped. Without a clean numbering system, pick errors, inventory discrepancies, and costly returns occur – especially critical in growing e-commerce, where an item is managed in parallel across shop, marketplace, and fulfillment partner.
In professional fulfillment, the SKU is far more than an internal number: it links master data, storage locations, barcodes, packing instructions, and cost calculations into a single, unique unit. Those who consciously separate, structure, and maintain SKU and article number lay the foundation for scalable warehouse processes – from your own basement warehouse to the fulfillment center.
Definition: What Is a SKU?
A SKU (Stock Keeping Unit) is the smallest unit by which a retailer or warehouse operator manages, books, and controls inventory. Each distinguishable product variant receives its own SKU – even if customers perceive the product as "the same item."
Typical distinguishing features for separate SKUs:
- Color, size, material, or version
- Packaging unit (single item vs. multipack)
- B-stock or refurbished status
- Batch or expiration date requirements for regulated goods
- Marketplace-specific bundles or sets
The SKU exists primarily internally – for warehouse, WMS, ERP, and fulfillment partners. Customers usually do not see it; it appears on delivery notes, pick lists, and warehouse codes.
Important: A SKU always describes exactly one bookable inventory unit. If a variant is changed (e.g., new label, different packaging), this is typically a new SKU – not an adjustment of the old one.
What Is an Article Number?
The article number is the overarching or alternative identifier of a product. Depending on company and industry, it can:
- be the SKU itself (small shops, single channel)
- represent a manufacturer or supplier number
- be an ERP-internal number without variant logic
- appear visibly to customers on invoices or in the shop
In mid-sized businesses, "article number" and "SKU" are often used synonymously. In professional fulfillment, a clear separation makes sense: The article number can designate the product family or base product, while SKUs represent the individual variants.
SKU vs. Article Number – The Comparison
SKU vs. Article Number vs. EAN – The Differences
Confusion between SKU, article number, EAN, and other codes is one of the most common sources of errors in fulfillment. Each code has its own purpose:
An EAN can be assigned to multiple SKUs (e.g., when bundling) – or conversely, one SKU can have multiple EANs (relabeling, reimport). Without documented mapping rules, this leads to scan errors during picking.
Structure and Naming of SKUs
A well-thought-out SKU schema saves time in the long run and prevents chaos during growth. Proven principles:
- Uniqueness: Each SKU may only exist once in the system – never reuse, not even for discontinued items.
- Readability: Staff should recognize variants from the code (e.g.,
HOODIE-BLK-Mfor Hoodie Black Size M). - No special characters: Hyphens and uppercase letters are common; avoid spaces, umlauts, and special characters (interface issues).
- Fixed structure: e.g.,
CATEGORY-COLOR-SIZEorBRAND-PRODUCT-VARIANT. - No hidden logic: What is not in the schema must be documented in master data.
Example Schema for Fashion Items
Tip: Plan the SKU schema before the first goods receipt. Subsequent renaming requires mapping tables, double bookings, and complex migrations – especially when switching to a 3PL partner.
SKU in the Fulfillment Process
The SKU runs through the entire order fulfillment process – from order to return:
Goods Receipt and Putaway
During goods receipt, each line item is booked by SKU. Suppliers often send their own article number – the system maps this to the internal SKU. With professional goods receipt, the ASN (Advance Shipping Notice) supports reconciliation: expected SKUs, quantities, and batches are known before arrival.
Picking and Scan Validation
The pick list shows the SKU per line item with storage location and quantity. When scanning at the shelf, the WMS checks: Does the scanned barcode match the expected SKU? Deviations block the process – a central mechanism for error prevention.
Packing and Shipping
Packing instructions, box sizes, and inserts are often stored per SKU. Heavy or fragile items receive different packaging logic than standard goods. The SKU on the shipping label and delivery note enables traceability for complaints.
Multi-Channel and SKU Mapping
Retailers selling in parallel in their own shop and on marketplaces need SKU mapping: One internal SKU can have multiple external references.
Typical mapping levels:
- Shop product ID → internal SKU
- Amazon ASIN / FNSKU → internal SKU
- eBay variant ID → internal SKU
- Supplier article number → internal SKU
Central SKU
Single source of truth for inventory and processes
Shop
Product ID ↔ internal SKU
Amazon
ASIN / FNSKU ↔ internal SKU
eBay
Variant ID ↔ internal SKU
ERP
Supplier article number ↔ internal SKU
Without a central SKU as "single source of truth," overselling (inventory sold twice) or underselling (inventory not offered) is at risk. In e-commerce fulfillment, end-to-end mapping is mandatory – not optional.
Best Practices for SKU Management
Master Data Maintenance
- Each SKU requires complete master data: weight, dimensions, EAN, packaging type, hazardous goods class (if relevant)
- Update changes to dimensions or packaging immediately – shipping costs and carrier rates depend on this
- Set discontinued SKUs to "inactive," do not delete (history for returns and reporting)
Barcodes and Labels
- Each SKU receives a unique warehouse label (barcode or QR)
- EAN on product and SKU label at storage location should be uniquely assignable
- For FIFO and LIFO strategies, maintain batch information in SKU master data or sub-items
Scaling and New Variants
When expanding the product range:
- Create new SKU according to fixed schema
- Maintain master data and packing instructions
- Assign storage location or adjust zone plan
- Update mapping in all sales channels
- Perform test pick and test shipment
Statistic: With increasing SKU complexity (from around 500 active SKUs without WMS), the pick error rate rises significantly – especially with poor master data maintenance. Clean schemas and complete master data keep the error rate stable even during growth.
Common Mistakes and How to Avoid Them
Duplicate SKUs for the same variant occur when teams create entries in parallel in shop and ERP. Solution: Define one system instance as master.
Reusing old SKUs for new products distorts sales and inventory history. Solution: Archive SKU, never recycle.
Missing variant SKUs – only one article number for all sizes – makes warehouse management impossible. Solution: Each sellable variant = own SKU.
No EAN mapping leads to manual entries at the packing station. Solution: Maintain EAN in master data and enable scan requirement.
Inconsistent naming makes search and reporting difficult. Solution: Written SKU guidelines and approval process for new numbers.
Checklist: Setting Up a SKU System
Before going live, the following points should be fulfilled:
- SKU naming schema documented and understood by the team
- Each sellable variant has its own unique SKU
- Master data complete (weight, dimensions, EAN, description)
- Warehouse labels with scannable code attached at location
- Multi-channel mapping aligned in shop, marketplaces, and WMS
- Packing instructions and packaging material defined per SKU
- Goods receipt with ASN reconciliation tested
- Trial pick and trial shipment completed without errors
KPIs Around SKU and Inventory
SKU quality affects measurable fulfillment metrics:
Frequently Asked Questions
Can a SKU Have Multiple EANs?
Yes, with documented mapping. Relabeling or reimport can result in a SKU having multiple EANs assigned – this assignment must be clearly stored in the system.
Must Each Variant Have Its Own SKU?
Yes, for bookable inventory management. Each distinguishable, sellable variant requires its own SKU with separate inventory.
What Happens When a SKU Is Renamed?
A mapping table links old and new numbers – the old SKU is not deleted to preserve history and return assignment.
SKU vs. Article Number – What Does the Customer See?
Usually neither; the customer sees the product name. SKU and article number are primarily internal control instruments.
How Many Characters Should a SKU Have?
6–20 characters, alphanumeric, without special characters – readable and interface-compatible.
Conclusion
SKU and article number are not administrative formalities, but the backbone of reliable fulfillment. A clear separation, a consistent naming schema, and complete master data enable error-free picking, precise inventory management, and scalable growth across all sales channels. Investment in SKU structure pays off from the first pick list to return processing – and prevents costly corrections in day-to-day operations.