IB Business Management SLTopic 1 — Growth and EvolutionPaper 1 & 2Core skill~10 min read
Why Bigger Is Cheaper, Until It Is Not
Big firms can usually make each item more cheaply than small firms can. That advantage is called economies of scale, and it is the main financial reason businesses want to grow. But it does not go on forever — grow too far and the cost of each item starts climbing again.
📘 What you need to know
Average cost is the cost of making one unit: total costs divided by output.
Economies of scale are the reasons average cost falls as a firm produces more.
Internal economies come from inside the business; external economies come from the industry growing around it.
At the bottom of the curve the firm is at productive efficiency — the lowest average cost it can reach.
Diseconomies of scale are the reasons average cost rises beyond that point: management, communication, distance and culture.
Total costs go up as output rises. It is the average cost that falls. Get this the wrong way round and the whole topic collapses.
The mechanism, in one picture
Every firm has costs that barely change however much it makes: the machine, the factory, the accountant, the advert. Make more units and those costs get shared out over more of them. That is the whole trick.
Learn this
Average cost = total costs ÷ output
The big factory buys more materials and pays more wages, so its total bill is far bigger. Each individual unit is still cheaper to make.
The error that costs marks. Students write that “costs fall as output rises”. They do not. Total costs rise, because you buy more materials and pay more wages. What falls is the average cost, because the fixed costs are spread more thinly.
The curve you need to be able to draw
Plot average cost against output and you get a U. The left side is economies of scale, the bottom is the cheapest the firm can ever be, and the right side is diseconomies of scale.
Practise sketching this from memory: axes labelled, curve U-shaped, dashed line at the lowest point, both regions named. It appears in exams as a two or three mark drawing.
Internal economies of scale
These come from growth inside the business, so the firm controls them.
Type
Why it lowers the average cost
Financial
Banks see large firms as safer, so they lend at lower interest rates. Cheaper borrowing means a lower cost attached to each unit
Managerial
A large firm can hire specialists — a full-time buyer, a full-time accountant. They do the job better than one manager doing five jobs badly
Marketing
One advertising campaign costs the same whether it sells 10,000 items or a million, and the same artwork can be reused in several regions
Purchasing
Buying materials in bulk earns a discount, so each unit of raw material costs less
Technical
Expensive machinery gets used closer to full capacity, so its cost is spread over far more units
Risk-bearing
A wider range of products means a flop in one line does not sink the firm, which lowers the cost of carrying that risk
External economies of scale
These come from the industry growing around the firm, so a single business cannot create them on its own — it just has to be in the right place.
Source
Why it lowers the average cost
Geographic cluster
Suppliers and repair firms move close to the big manufacturers, so parts arrive faster and transport bills fall. Car-making regions often support thousands of these smaller firms
Transport links
Roads, rail and airports get built to serve a growing industry, which cuts the cost of moving staff and goods
Skilled labour pool
Local colleges start training the workers the industry needs, so firms spend less on recruiting and training
Favourable legislation
Governments support industries they want to grow, through grants, tax breaks or lighter rules, all of which reduce costs
Quick test in an exam: ask yourself whether the firm could have caused it alone. Bulk buying, yes — internal. A new motorway, no — external.
Diseconomies of scale
Keep growing and the problems start. Every one of them is really the same problem: a big organisation is harder to run than a small one.
Type
What goes wrong
Management
Managers start acting in their own interest rather than the firm’s, becoming territorial and blocking each other. Efficiency drops and average cost rises
Communication
More layers of management means messages get slower and more distorted, so problems are fixed late and expensively
Geographical
Sites spread across many places create logistical headaches and make coordination harder
Cultural
Expanding abroad brings different working norms and expectations, which disrupts production while everyone adjusts
Worked examples
WORKED EXAMPLE
Define the term economies of scale. [2]
Say what happens, then say whyEconomies of scale are the cost advantages a firm gains as it increases its scale of output, causing average cost per unit to fall.Second element:They arise because fixed costs are spread over more units and because large firms can buy and borrow more cheaply.2 marks
WORKED EXAMPLE
A firm makes 5,000 units at a total cost of 250,000. It expands to 10,000 units and total costs rise to 420,000. Calculate the average cost at each level and comment. [4]
Step 1: before expandingAverage cost = 250,000 ÷ 5,000 = 50 per unitStep 2: after expandingAverage cost = 420,000 ÷ 10,000 = 42 per unitAverage cost falls by 8 per unitStep 3: commentTotal costs rose by 170,000, but output doubled, so the firm is benefiting from economies of scale. Say both halves — total up, average down.
WORKED EXAMPLE
The same firm expands again to 20,000 units and total costs reach 900,000. Explain what has happened. [4]
Step 1: work out the new average costAverage cost = 900,000 ÷ 20,000 = 45 per unitAverage cost has risen from 42 to 45Step 2: name it
The firm has passed the bottom of its long run average cost curve and is now suffering diseconomies of scale.Step 3: give a reasonExtra layers of management have slowed communication and decisions, so the firm is less efficient than it was at 10,000 units.
💡 Exam tip
Always divide. If a question gives total costs and output, calculate average cost before you say anything about scale.
Name the type. “Purchasing economies, because bulk orders earn a discount” scores far more than “economies of scale”.
Internal or external? State which, every time. It is a quick way to show precision.
Learn to sketch the U curve with both axes labelled and both regions named.
Use diseconomies in evaluation. They are the built-in argument against growing further.
⚠ Common mix-up
Total costs do not fall. Only average cost falls. This is the single most common error in the topic.
Economies of scale are not the same as high profits. They lower cost per unit; whether that becomes profit depends on price.
Diseconomies are not caused by making mistakes. They come from size itself — more people, more layers, more distance.
External economies are not the same as external growth. One is about industry conditions, the other is about mergers.
The bottom of the curve is not a maximum. It is the lowest average cost, also called productive efficiency.
Up next: Should a Business Grow at All? — cheaper units are only one part of the argument, and plenty of successful firms decide to stay exactly the size they are.
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