The purpose of inventory control charts

Inventory control charts are graphical tools that businesses use to track and manage their stock levels over time. These charts plot data such as the quantity of goods in stock, incoming deliveries, minimum safety levels, and upper limits for holdings. By visualising this information, they help managers make informed decisions about when and how much to order, ensuring that stock is available without tying up too much capital.

How inventory control charts support stock management

• Determining order timing and quantity - The charts show patterns in stock usage, allowing managers to identify the best moments to place orders and the ideal amounts to purchase, which can minimise costs and avoid shortages.
• Analysing unusual events - They enable businesses to simulate the impact of unexpected situations, such as a rival's effective marketing drive that boosts demand for similar products, helping to predict and adjust stock levels accordingly.

Key features of inventory control charts

Inventory control charts include several important elements that reflect different aspects of stock management. These features help businesses maintain efficient operations by balancing the risks of running out of stock against the costs of holding too much.

Main components and their influences

• Buffer inventories - These are minimum stock levels kept as a safety net to cover uncertainties, such as delays in deliveries or fluctuations in production. Higher buffers are needed if suppliers are unpredictable or if stopping and restarting operations is expensive, as this reduces the risk of costly downtime.
• Maximum inventory level - This represents the highest amount of stock a business aims to hold, often constrained by storage space or the financial burden of excess holdings. It can be calculated by adding the economic order quantity (the most cost-effective amount to order) to the buffer level for each item.
• Re-order quantity - This is the amount ordered each time stock needs replenishing, typically based on the economic order quantity to optimise costs like ordering fees and holding expenses.
• Lead time - The duration between placing an order and receiving it affects planning; longer or unreliable lead times require higher re-order points and larger buffers to prevent stockouts.
• Re-order level:
  • This is the stock point at which a new order should be placed, determined by the rate at which items are used and the expected delivery time.
  • Many businesses use computer systems to monitor sales and deliveries in real-time, automatically triggering orders when levels hit this point.
  • These systems generate digital versions of the charts for easy analysis.

Real-world applications of inventory control charts

In actual business scenarios, inventory control charts rarely follow perfectly straight lines due to variable demand and supply factors. For instance, a company selling seasonal clothing might see sharp drops in stock during a heatwave, resulting in steep declines on the chart. These tools are valuable for reviewing past patterns and planning ahead, such as adjusting buffer levels based on historical spikes or dips.