Economies and Diseconomies of Scale

Updated for the 2026-2027 CFA® Level I curriculum.

A firm's per-unit cost does not stay fixed as it grows. As output expands over the long run, unit costs can fall, hold steady, or rise depending on how efficiently the firm scales its operations. CFA Level I tests whether you can read this pattern from a long-run average cost curve and explain what drives it. This note covers economies and diseconomies of scale, the two forces behind that pattern.

Key Takeaways

• Economies of scale mean LRAC falls as output rises. Diseconomies of scale mean LRAC rises as output rises.

• The LRAC curve is the least-cost envelope of every possible short-run plant size, not one fixed short-run curve.

• Minimum efficient scale is the lowest output level at which LRAC reaches its minimum.

• Constant returns to scale describe the flat middle section where unit cost barely changes.

• Economies of scale come from specialization, better technology, bulk purchasing, and spreading fixed costs. Diseconomies come from coordination problems and management complexity.

• Economies of scale differ from diminishing marginal returns. Diminishing returns is a short-run concept tied to one fixed input.

• Scale effects apply under both perfect and imperfect competition, but the competitive impact differs.

What You Need to Know for CFA Level I

• Recognize economies, constant returns, and diseconomies directly from the slope of LRAC.

• Understand that the long run allows the firm to change all inputs, including plant size.

• Treat LRAC as the lower envelope of multiple short-run average total cost curves.

• Identify minimum efficient scale as a specific output level, not a maximum limit.

• Explain the operational reasons unit costs fall or rise as scale changes.

• Separate economies of scale from increasing returns to scale and from diminishing marginal returns.

• Apply scale reasoning to firms in both perfectly and imperfectly competitive markets.

What Are Economies of Scale?

Economies of scale exist when a firm's long-run average cost falls as it produces more output. On a graph, this shows up as a downward-sloping LRAC curve. Because the long run allows every input, including plant size, labor force, and equipment, to change, the firm is not stuck with one fixed setup. It can redesign its entire operation to fit a larger output level.

Several operational forces drive economies of scale:

• Specialization. Larger output lets workers and machines focus on narrower tasks, which raises efficiency.

• Better technology. Larger plants can justify equipment that small plants cannot afford to use efficiently.

• Purchasing power. Higher volume lets a firm negotiate lower input prices.

• Information systems. Larger firms can spread the cost of planning, scheduling, and data systems across more units.

• Indivisible costs. Costs like a factory roof or a base software license stay fixed in total, so per-unit cost drops as output rises.

What Are Diseconomies of Scale?

Diseconomies of scale exist when long-run average cost rises as output increases further. This shows up as an upward-sloping LRAC curve. The firm has grown past the point where added output improves efficiency.

Common causes include:

• Coordination problems. More output usually means more locations, teams, or product lines to manage together.

• Extra management layers. Larger firms often need more supervisors and more approval steps, which adds cost without adding output.

• Duplicated functions. Multiple divisions may repeat the same administrative or support tasks.

• Communication delays. Information takes longer to move through a larger organization, which slows decisions.

• Input constraints. Some inputs, such as skilled managers or specialized suppliers, become harder to source in the needed quantity.

These causes are general operating patterns. They are not proof that any specific company will fail at scale.

Economies of Scale vs Diseconomies of Scale

The direction of the LRAC slope is the identification rule. If unit cost is falling, the firm is in the economies-of-scale range. If unit cost is flat, it is near constant returns. If unit cost is rising, the firm is in the diseconomies-of-scale range.

How the Long-Run Average Cost Curve Works

The short run is a period with at least one fixed input, usually plant size. The long run is a planning horizon where every input can change. This distinction matters because it defines which cost curve applies.

Each possible plant size has its own short-run average total cost (SRATC) curve. The LRAC curve is the lower envelope of all these SRATC curves. At each output level, LRAC shows the lowest average cost achievable using the best available plant size for that output. The firm does not move along one fixed SRATC curve as output grows across the long run. Instead, it selects a different plant size, and therefore a different SRATC curve, for each output level it plans to produce.

Where:

• = total cost of production at the least-cost plant size for output Q

• = quantity of output produced

Minimum Efficient Scale and Constant Returns to Scale

Minimum efficient scale is the lowest output level at which the firm reaches the minimum point on its LRAC curve. Below this output, the firm has not captured all available economies of scale. Its unit cost is higher than it could be at a larger plant size.

Beyond minimum efficient scale, output can enter a flat region where unit cost barely changes. This is constant returns to scale. Output pushed further, into the upward-sloping region, exposes the firm to diseconomies of scale.

Under perfect competition, firms cannot set price above the market level. Long-run survival depends on operating at or near minimum efficient scale, since a firm producing at a higher-cost point on LRAC cannot compete on price with firms that have reached the efficient scale.

Why Scale Affects Costs

Scale affects cost because it changes how efficiently a firm converts inputs into output. Rising output can allow better use of specialized labor, equipment, and bulk input pricing, which lowers unit cost. Past a certain point, the same rising output creates coordination and management burdens that raise unit cost. The LRAC curve captures both effects across the full range of possible output levels.

Perfect vs Imperfect Competition

Scale changes cost structure under both perfect and imperfect competition, but the strategic impact differs.

Under perfect competition, firms take the market price as given. Because there is no pricing power, cost efficiency is the main lever available to the firm. Operating near minimum efficient scale supports long-run survival in this structure.

Under imperfect competition, a lower cost base from scale can support stronger margins or more flexible pricing. Demand conditions and competitor behavior still determine whether that cost advantage turns into higher profit. Larger scale on its own does not guarantee stronger margins or market power.

Worked Interpretation Example

Northfield Packaging is evaluating six possible output levels for a new production line. Long-run average cost at each level is shown below.

Step 1: Identify the economies-of-scale range. LRAC falls from $18 to $12 as output rises from 10,000 to 30,000 units. This is the economies-of-scale range.

Step 2: Identify minimum efficient scale. LRAC first reaches its minimum of $12 at 30,000 units. This is minimum efficient scale.

Step 3: Identify the constant-cost region. LRAC stays at $12 from 30,000 to 40,000 units. This is the constant returns to scale range.

Step 4: Identify the diseconomies-of-scale range. LRAC rises from $12 to $16 as output increases from 40,000 to 60,000 units. This is the diseconomies-of-scale range.

Analyst interpretation: Northfield minimizes unit cost between 30,000 and 40,000 units. If current output is 50,000 or 60,000 units, the firm should scale back toward that range unless demand strongly justifies the higher cost. Expanding beyond 40,000 units raises cost per unit without an efficiency benefit.

Common Exam Traps

Treating economies of scale as a short-run labor change. Economies of scale are a long-run concept tied to changing plant size and all inputs, not just adding workers to a fixed plant.

Confusing diseconomies of scale with diminishing marginal returns. Diminishing marginal returns is a short-run concept that occurs with at least one fixed input. Diseconomies of scale occur in the long run when all inputs can change.

Assuming every output increase lowers unit cost. This is only true in the economies-of-scale range. Past minimum efficient scale, further output can raise or hold unit cost steady.

Calling the entire U-shaped LRAC curve an economy of scale. Only the downward-sloping section represents economies of scale. The flat and upward-sloping sections represent constant returns and diseconomies.

Assuming minimum efficient scale is the maximum possible output. Minimum efficient scale is the lowest output that reaches minimum LRAC, not an upper limit.

Equating greater scale with guaranteed profitability or market power. Scale changes cost structure. Demand, pricing, and competitive conditions still determine profitability.

Practice Question

Three packaging firms operate along the same industry LRAC curve. Firm A produces at an output level where LRAC is still falling. Firm B produces at the output level where LRAC reaches its minimum. Firm C produces at an output level where LRAC is rising. Which firm should increase output to reduce its long-run average cost per unit?

1. Firm A

2. Firm B

3. Firm C

FAQs About Economies and Diseconomies of Scale