Inventory Management
Also: Warenwirtschaftssystem · WWS
Inventory management is the end-to-end control and recording of all goods movements in a business – from purchasing through storage to sales. An inventory management system (WWS) maps this goods flow digitally and keeps stock levels up to date in real time.
Inventory management is the operational control and documentation of all goods movements along the chain of purchasing, storage and sales. An inventory management system (WWS) maps these processes digitally: it manages items, posts goods receipts and issues, keeps stock levels in real time, and links purchase orders with supplier data, sales orders and documents. The goal is to know at any moment which goods are available in what quantity and where, and how they move through the business.
The term is often used interchangeably with "inventory management system" or the German abbreviation "WWS". At the core of every system is stock management, which makes every change in inventory traceable through quantity- and value-based postings. This makes inventory management the operational backbone for retail, wholesale and e-commerce: it prevents stockouts and overstocks, speeds up order processing, and provides the data foundation for replenishment and analysis.
At a glance
- Controls the entire goods flow: purchasing, warehouse, sales, goods receipt and goods issue
- Keeps stock in real time by quantity and value
- A WWS is a subset of ERP – more narrowly focused on goods and inventory
- Key metrics: inventory value, stock turnover, days of supply, service level
- Essential for multi-channel retail and e-commerce with many channels
What an inventory management system does
An inventory management system brings the core operational functions of retail together in one place. In purchasing it manages suppliers, creates purchase orders and tracks their status through to delivery. In the warehouse it records stock by item, storage location and, where relevant, batch or serial number. In sales it turns quotes into orders, reserves goods and triggers delivery and invoicing.
These areas are connected by two posting processes: goods receipt, which adds incoming deliveries to stock and reconciles them against the purchase order, and goods issue, which deducts the sold quantity during picking and shipping. Each of these postings updates stock immediately. This creates a consistent, end-to-end picture of the goods – from the order placed with the supplier to delivery to the customer.
The basis for all these processes is the item master: the central collection of all product data such as item number, description, units, prices, suppliers and storage locations. Without clean master data, a WWS can neither plan replenishment correctly nor post reliably.
The goods flow from purchasing to shipping
The typical goods flow begins with replenishment planning: based on sales, minimum stock and open orders, the system determines demand and proposes purchase orders. Demand becomes a purchase order to the supplier, whose terms and delivery dates the WWS monitors.
When the goods arrive, they are checked at goods receipt and posted to stock – ideally reconciled against the purchase order to spot quantity or price discrepancies immediately. The goods are stored and assigned to a storage location. On the sales side, a customer order – from the store, the online shop or a marketplace – triggers a reservation. During picking, the goods are removed, posted out at goods issue and shipped; in parallel, a delivery note and invoice are generated.
This cycle closes continuously: every sale reduces stock, every delivery replenishes it. Because the WWS logs every movement, the goods flow remains fully traceable – a prerequisite for reliable delivery commitments and proper bookkeeping.
Stock management and key metrics
The heart of inventory management is stock management. It records stock both by quantity (how many units are in the warehouse) and by value (how much capital that stock ties up). Besides physical stock, a WWS usually distinguishes between available, reserved and ordered stock so that goods are not sold twice. Periodic or perpetual stocktaking reconciles system stock with reality.
From this data the system derives metrics that make the profitability of the warehouse measurable. Stock turnover shows how often inventory is sold per year; days of supply indicates for how many days stock is expected to last. The average inventory value and tied-up capital reveal how much money is locked in the warehouse. The service level measures what share of demand can be served immediately.
Typical warehouse metrics
Stock turnover = cost of goods sold ÷ average inventory. Days of supply = stock ÷ average daily sales. Both help balance tied-up capital against shortages. Together with reorder points they form the basis of data-driven replenishment planning.
Inventory management vs. ERP – the distinction
Inventory management and ERP are often equated, but they are not the same. An inventory management system focuses on the goods flow: purchasing, warehouse, stock and sales. An ERP system (Enterprise Resource Planning) plans and controls all of a company's resources beyond that – additionally covering financial accounting, cost accounting, HR, production and often CRM. Inventory management is therefore a subset of ERP: every ERP contains inventory management functions, but not every WWS is a full ERP.
In practice the boundaries blur. Many modern systems start as inventory management and are extended with accounting, manufacturing or business intelligence until they effectively reach ERP scope. For small retailers a pure WWS with connected accounting is often enough; as the company grows and requirements for controlling, production or multiple sites increase, the move to ERP is the logical next step.
The choice depends less on the label than on actual needs: those who mainly move and sell goods need strong inventory management. Those who also want to plan, post and analyse company-wide need an ERP.
Relevance for retail and e-commerce
In retail, inventory management determines delivery reliability and margin. Stockouts lead to rejected orders and lost customers, overstocks tie up capital and warehouse space. A WWS keeps both extremes in balance by making stock transparent and supporting replenishment with data.
A capable WWS is indispensable especially in e-commerce and multi-channel retail. Anyone selling at once through their own online shop, several marketplaces and in-store must keep stock synchronised across channels – otherwise overselling looms. The system consolidates orders from all channels, maintains a shared stock level, and reports stock changes back to the connected shops. Typical functions therefore include interfaces to shop systems and marketplaces, automated order and document processing, batch and serial number management, returns handling, and connections to shipping providers and accounting. Cloud-based inventory management additionally simplifies access from multiple sites and the quick connection of new sales channels.
Example
Example: multi-channel retailer with 6,000 items
A mid-sized retailer of household goods sells through its own online shop, two marketplaces and a small store. Before introducing a WWS, the team maintained stock in separate lists – with the result that popular items were sold simultaneously across several channels even though only one unit remained in the warehouse. The overselling led to cancellations, frustrated customers and poor reviews.
With a central inventory management system, all channels now run on a shared stock level. A sale in the shop immediately reduces the available quantity on the marketplaces. Goods receipts are checked against the purchase order and posted automatically; metrics such as days of supply and stock turnover drive reordering. The result: no more overselling, shorter lead times and a solid foundation for accounting.
Frequently asked questions
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