What a supply chain actually is

A supply chain is the network of organizations, people, resources, information and activities involved in moving a good or service from its initial inputs to the final customer. It’s much more than delivery trucks. The network includes suppliers, the business itself, storage and transport, distributors, retailers, digital ordering systems and the information that passes between them.

The supply chain process is a sequence of connected operational stages that turns inputs into products and gets them to places where customers can buy or receive them. In a simple version, suppliers provide raw materials or components, then the business transforms them. Logistics handles storage and movement, while distributors or retailers help the goods reach customers. Feedback and sales data flow back up the chain.

A local supply chain mainly relies on suppliers, production and distribution within a nearby region or country. These supply chains are usually shorter and easier to monitor, with less exposure to international transport delays. They may support local employment and reduce transport-related environmental impact. However, local suppliers may charge higher prices or have less capacity.

A global supply chain uses suppliers, production or distribution across national borders. It can lower costs, offer a wider choice of suppliers and provide access to specialist components or labour. That comes with added complexity, including exchange-rate risk, customs delays and political risk. Lead times may be longer, communication issues can arise, and the chain is more vulnerable to disruption.

At this point, production planning becomes managerial rather than purely operational. When choosing between local and global supply chains, a business must balance cost, speed and reliability against flexibility, quality and sustainability. A low-cost global supplier isn’t automatically the better option if delays cause stock-outs and leave customers unhappy.

Two very different attitudes to stock

Stock control means managing inventory levels so a business can keep operating without holding more materials or finished goods than it needs. Inventory is often used to mean the same thing, particularly when referring to raw materials, work-in-progress and finished goods.

Just-in-time (JIT) is a stock control method where inputs arrive only when needed, and goods are produced only when there is demand. It follows a lean approach: storage falls, less cash is tied up in stock, fewer items become obsolete and waste is often reduced.

Just-in-case (JIC) is a stock control method that holds extra stocks of inputs or finished goods as protection against uncertainty. The focus is security. If demand rises suddenly, a supplier delivers late or transport is disrupted, stock remains available.

Comparison of JIT and JIC stock control methods.

JIT usually suits businesses that have reliable suppliers and predictable processes, backed by strong communication systems and a culture of continuous improvement. Cash flow can improve because money isn’t sitting on shelves. However, the system becomes fragile when deliveries fail. Even a small disruption can bring production to a complete stop.

JIC is more likely to suit businesses dealing with uncertain demand, long lead times, fragile supply chains or seasonal peaks. It may also be suitable for essential products where stock-outs would cause serious damage. The risk of running out falls, but storage, insurance and handling costs rise. So does the risk of wastage or obsolescence.

The best answer is rarely “JIT is better” or “JIC is safer”. It depends on the business. A bakery using perishable ingredients won’t necessarily make the same stock decision as a hospital managing critical supplies or a manufacturer that relies on imported micro-components.

Reading the stock control chart

A stock control chart tracks changes in inventory levels over time. It also shows when a business should place an order and when that order should arrive. Stock level, usually measured in units, appears on the vertical axis. Time, such as days or weeks, runs along the horizontal axis.

A lead time is the interval between placing an order and receiving the stock. For example, if a supplier delivers five days after the order is placed, the lead time is five days. A longer lead time usually requires the business to reorder earlier.

Buffer stock is the minimum reserve of inventory a business keeps to reduce the risk of running out. It isn’t “spare stock for fun”. Instead, it protects the business when deliveries arrive late or demand is unexpectedly high.

A reorder level is the stock level that triggers a new order. In a simple stock control model:

A reorder quantity is the number of units ordered whenever stock reaches the reorder level. If this quantity is too low, the firm must order too often and may incur higher administration or delivery costs. If it is too high, the firm ends up holding too much stock.

Read a stock control chart by following the line. As the business uses or sells stock, the level falls. An order is placed when it reaches the reorder level, but stock continues to fall during the lead time. With accurate planning, the delivery arrives before the stock level drops below buffer stock. Higher-than-expected demand or a late supplier forces the business to use its buffer stock. Once that buffer is exhausted, the business has a stock-out.

When drawing the chart, make sure the sequence makes sense. Stock should fall gradually as it is used, then rise suddenly when a delivery arrives. It should never magically increase before the delivery date. The vertical jump when new stock arrives represents the reorder quantity.

How fully the business is using its productive capacity

Capacity means the maximum output a business can produce in a given time period with the resources it has available. In a factory, this might be units per week; in a hotel, rooms available per night. A call centre may measure it as calls handled per hour.

The Capacity utilization rate measures, as a percentage, how much of that maximum productive capacity the business is actually using.

When the capacity utilization rate is below 100%, the business has spare capacity. This gives it room to respond if demand rises. However, resources may be underused, with fixed costs spread over fewer units. A rate close to 100% may appear efficient, but it leaves little room for maintenance, staff training, urgent orders or errors.

Managers use the ratio to decide whether to increase output, invest in new capacity, reduce capacity, outsource some production or stimulate demand. The figure is most useful when compared over time, with competitors or against the firm’s own target level.

Measuring production that fails to meet the standard

A defect is a unit of output that doesn’t meet the required quality specification. It may be unsafe, damaged, incomplete or inaccurate. It could also fall below the agreed standard.

Defect rate measures the percentage of total output that is defective.

A low defect rate suggests a reliable production process, but it doesn’t prove that customers are satisfied. A high rate creates costs through reworking, scrapping, refunds and warranty claims. Defects can also cause delays, reputational damage and sometimes legal risk.

When interpreting the figure, the key word is “compared”. A 2% defect rate may be excellent in one industry but unacceptable in another. Quality expectations differ greatly for a medicine producer, an aircraft component supplier and a handmade craft producer.

Productivity is about output from inputs

Productivity measures efficiency by comparing the output produced with the inputs used. This differs from production. Production asks, “How much did we make?” Productivity asks, “How efficiently did we make it?”

Productivity rate compares total output with total input and expresses the result as a percentage.

Labour productivity measures the output produced per unit of labour input.

Training, better motivation, improved technology, clearer job design or better-quality inputs can raise labour productivity. The figure may also increase when the least productive workers leave, so it needs careful interpretation. Ratios show what changed; they don’t automatically explain why.

Capital productivity measures the output or revenue generated per unit of capital input. Working capital productivity is commonly calculated as follows:

A higher figure suggests that the business generates more sales from the capital tied up in its day-to-day operations. A very high figure, though, may show that working capital is too low. That could cause liquidity problems.

Operating leverage is a ratio showing how the business’s fixed-cost structure makes operating profit sensitive to changes in output.

A business has high operating leverage when fixed costs make up a high proportion of its costs compared with variable costs. With strong sales, profit can rise quickly because the fixed costs have already been covered. If demand falls, profit can drop sharply for the same reason. This links directly to break-even thinking: fixed costs are powerful, but not always comfortable.

Calculating the buying option

Cost to buy (CTB) is the total purchase cost of a product or component obtained from an external supplier.

CTB helps with a make-or-buy decision. When buying costs less than making, using a supplier may look like the sensible choice. The calculation isn’t the whole decision, though. Managers also need to weigh supplier reliability, quality, delivery times and transport costs. Other concerns include exchange-rate risk, loss of control, confidentiality, and whether buying would free up capacity for something more profitable.

Buying is often attractive if the supplier benefits from economies of scale, specialist expertise or better technology. However, it can be risky if the product is strategically important or a supply chain disruption would badly damage the business.

Calculating the making option

Cost to make (CTM) is the total internal production cost of producing a product or component within the business.

The basic financial comparison is straightforward. Compare CTM with CTB for the same quantity and quality. Making is financially attractive when CTM is lower; buying is financially attractive when CTB is lower.

The formula doesn't capture the whole decision. Making may improve quality control and allow faster design changes. It can also protect know-how and reduce dependence on suppliers. On the other hand, it may require investment and specialist labour, as well as management time and capacity that could be used elsewhere.

Production planning therefore combines operations, finance and strategy. The cheapest option on paper may not be the best once reliability, quality, flexibility and long-term control are considered.