SKU and Article Numbers: Essential Guide for Online Stores

If you sell products online, you have almost certainly encountered the terms SKU and article number. These identifiers sit at the foundation of every successful e-commerce operation, yet many store owners treat them as an afterthought. They paste random numbers into spreadsheets, copy manufacturer codes without thinking, or skip product identification entirely until chaos erupts in the warehouse. This guide explains what SKUs and article numbers actually are, how they differ from other product identifiers, and how to build a system that keeps your inventory accurate as your business grows.

What Exactly is a SKU?

SKU stands for Stock Keeping Unit. It is a unique alphanumeric code that identifies a specific product variant in your inventory system. The key word here is variant. A blue t-shirt in size M and the same blue t-shirt in size L are different SKUs, even though they share the same product name, brand, and design. Every distinct combination of attributes that affects which physical item gets pulled from the shelf needs its own SKU.

Unlike barcodes or manufacturer part numbers, SKUs are internal. You create them according to your own logic. There is no global registry, no standard format, and no authority that issues them. This means you have complete freedom to design a system that makes sense for your specific business and product catalog. It also means that two different companies will have completely different SKUs for the same product.

For example, if you sell running shoes, a well-designed SKU might look like this: RS-NKE-AM90-BLK-42. This encodes the category (Running Shoes), brand (Nike), model (Air Max 90), color (Black), and size (42). A warehouse worker who sees this code on a pick list immediately knows what to look for and where to find it, even without checking the product name in the system.

Article Number vs SKU: What is the Difference?

In many markets, especially in Eastern Europe, the term "article number" is used interchangeably with SKU. Technically, though, there are nuances. An article number often refers to the manufacturer's or supplier's product code. It identifies the product from the supplier's perspective. The SKU, on the other hand, is your internal code that identifies the product from your warehouse and sales perspective.

In practice, many small online stores use supplier article numbers as their SKUs. This works fine when you have a single supplier per product. Problems arise when you source the same product from multiple suppliers (each with their own article number) or when different suppliers use the same article number for different products. At that point, you need your own SKU system that serves as the single source of truth.

There are also other identifiers in the product ecosystem that should not be confused with SKUs. UPC (Universal Product Code) and EAN (European Article Number) are standardized barcodes issued through GS1. They identify the product universally across all retailers and systems. An ISBN identifies books. An ASIN is Amazon's internal product identifier. None of these replace the need for your own SKU system, though they can coexist alongside it.

Why SKUs Matter for E-commerce Operations

The importance of a proper SKU system grows exponentially with the size of your catalog and order volume. Here are the core reasons SKUs are essential for any serious online store.

Inventory accuracy: When every product variant has a unique identifier, counting stock becomes straightforward. You know exactly how many units of each specific item are on the shelf, in transit, reserved for pending orders, or returned. Without SKUs, inventory counts devolve into guesswork, and guesswork leads to overselling, stockouts, and unhappy customers.

Warehouse efficiency: Picking errors are one of the most expensive mistakes in e-commerce logistics. Sending the wrong size, wrong color, or wrong product entirely creates a cascade of costs: return shipping, repacking, customer service time, and lost trust. SKU-based picking with barcode verification reduces error rates to below 0.5% at well-run fulfillment centers like MTP Group.

Sales analytics: SKU-level sales data tells you which specific product variants are selling, which are sitting on shelves, and which have high return rates. This granularity is impossible without proper product identification. Knowing that "blue t-shirts" sell well is useful. Knowing that the blue t-shirt in size M outsells size XL by three to one is actionable intelligence for purchasing decisions.

Multi-channel selling: If you sell on your own website, Rozetka, Prom.ua, and Instagram simultaneously, SKUs are the bridge that keeps inventory synchronized. Each channel may use its own internal identifiers, but your SKU is the common thread that connects everything in your warehouse management system.

How to Create an Effective SKU System

Designing a good SKU system is a one-time investment that pays dividends for years. Here are the principles that experienced operators follow.

Start with the broadest category and narrow down. The first characters of your SKU should identify the product category, followed by brand, model, and variant attributes. This creates a natural hierarchy that makes sorting and searching intuitive.

Keep it human-readable. The best SKUs can be decoded by a person without looking them up in the system. Use meaningful abbreviations: BLK for black, WHT for white, SM for small, LG for large. Avoid purely numeric sequences that carry no visual meaning.

Use consistent delimiters. Hyphens or dots between segments improve readability. RS-NKE-BLK-42 is much easier to read than RSNKEBLK42, especially on a small warehouse scanner screen or a printed pick list.

Avoid ambiguous characters. The letter O and number 0, the letter I and number 1, the letter S and number 5 are frequently confused in manual operations. Either exclude them entirely or use a font in your warehouse system that clearly differentiates them.

Plan for growth. If your current catalog has 200 products, design a system that can handle 2,000 or 20,000. Leave room in your code structure for new categories, brands, and attributes. Rebuilding a SKU system after it outgrows its design is a painful, error-prone process that disrupts operations for weeks.

SKU Management in a Fulfillment Context

When you work with a professional fulfillment operator, SKU management becomes a shared responsibility. During the onboarding process at MTP Group, each product is assigned a location in the warehouse management system, mapped to your sales channel identifiers, and labeled with a scannable barcode if one does not already exist.

The fulfillment center uses your SKUs as the primary identifier for all warehouse operations: receiving, shelving, picking, packing, and returns processing. Every time a product is touched, it is scanned, and that scan event is logged against the SKU. This creates a complete audit trail that shows exactly when each unit arrived, where it was stored, when it was picked, and which order it went into.

For sellers who arrive without any SKU system, MTP Group can create one during onboarding. The team analyzes your product catalog, identifies the attributes that need to be encoded, and generates a consistent SKU structure. This is included as part of the standard onboarding process and typically takes one to two business days.

Common SKU Mistakes to Avoid

Over years of working with online stores, certain patterns of SKU mismanagement appear repeatedly. Avoid these common traps.

Using the supplier's code as your only identifier. This breaks the moment you change suppliers, source from multiple suppliers, or the supplier changes their numbering system. Always maintain your own SKU layer on top of supplier codes.

Making SKUs too long. Codes exceeding 16 characters become unwieldy. Warehouse staff make more errors typing or reading them, barcode labels need to be larger, and database fields fill up faster. Aim for 8 to 12 characters.

Reusing SKUs of discontinued products. When a product is removed from your catalog, retire its SKU permanently. Reusing it for a new product creates confusion in historical sales data and can cause fulfillment errors if old stock is still in the warehouse.

Encoding volatile information. Do not put the price, warehouse location, or season into the SKU. Prices change frequently. Products get moved to different shelves. Seasonal codes become meaningless in the off-season. Encode only the product's inherent, stable attributes: category, brand, model, color, size.

A well-designed SKU system is invisible when it works. You only notice it when it is broken, and by then, it has already cost you money in errors, delays, and lost inventory.

SKUs and the Ukrainian E-commerce Market

In Ukraine, the SKU discipline gap between large retailers and small online stores remains significant. Major marketplaces like Rozetka enforce structured product data, but independent sellers on Prom.ua, Instagram, and their own websites frequently operate with minimal or no product identification systems. This becomes a critical bottleneck when order volumes grow beyond what one person can manage from memory.

The shift toward professional fulfillment services is pushing more Ukrainian sellers to implement proper SKU systems for the first time. When your products are stored and shipped by an external partner, you cannot rely on personal knowledge of which product is in which box. The system must be explicit, codified, and scannable. This is ultimately a positive development that forces operational maturity.

MTP Group works with sellers at every stage of SKU readiness, from those who have comprehensive systems already in place to those who are starting from scratch with a spreadsheet of product names. The infrastructure is designed to handle it all, and the onboarding team ensures every product is properly identified before the first order ships.