What is the Shape of the Average Long-Run and Short-Run Cost Curves?

While in the short run firms are limited to operating on a single average cost curve (corresponding to the level of fixed costs they have chosen), in the long run when all costs are variable, they can choose to operate on any average cost curve. Thus, the long-run average cost (LRAC) curve is actually based on a group of short-run average cost (SRAC) curves, each of which represents one specific level of fixed costs. More precisely, the long-run average cost curve will be the least expensive average cost curve for any level of output.

We build the long-run average cost curve from a group of short-run average cost curves. Five short-run-average cost curves appear on the diagram. Each SRAC curve represents a different level of fixed costs. For example, you can imagine SRAC₁ as a small factory, SRAC₂ as a medium factory, SRAC₃ as a large factory, and SRAC₄ and SRAC₅ as very large and ultra-large. Although this diagram shows only five SRAC curves, presumably there are an infinite number of other SRAC curves between the ones that we show. Think of this family of short-run average cost curves as representing different choices for a firm that is planning its level of investment in fixed cost physical capital—knowing that different choices about capital investment in the present will cause it to end up with different short-run average cost curves in the future.

The long-run average cost curve shows the cost of producing each quantity in the long run, when the firm can choose its level of fixed costs and thus choose which short-run average costs it desires. If the firm plans to produce in the long run at an output of Q₃, it should make the set of investments that will lead it to locate on SRAC₃, which allows producing q₃ at the lowest cost. A firm that intends to produce Q₃ would be foolish to choose the level of fixed costs at SRAC₂ or SRAC₄. At SRAC₂ the level of fixed costs is too low for producing Q₃ at lowest possible cost, and producing q₃ would require adding a very high level of variable costs and make the average cost very high. 

At SRAC₄, the level of fixed costs is too high for producing q₃ at lowest possible cost, and again average costs would be very high as a result.

The shape of the long-run cost curve is fairly common for many industries. The left-hand portion of the long-run average cost curve, where it is downward- sloping from output levels Q₁ to Q₂ to Q₃, illustrates the case of economies of scale. In this portion of the long-run average cost curve, larger scale leads to lower average costs. 

Relate Topics

• Theory of the Firm
• Capital Formation
• Rent Seeking
• Structure Conduct Performance Model
• Integration
• Co-Insurance Effect
• Conglomerates
• Cost vs Profit Center
• Accelerator Theory
• Market Structure
• Fixed Cost vs Variable Cost
• Actual vs Implicit Costs
• Explicit Costs
• True Cost Economics
• Accounting Profit
• Economic Profit
• What are Factors of Production?
• Factor Income
• Production Function
• Fixed and Variable Inputs
• Short-Run and Long-Run Production
• Short Run
• Total Product
• Marginal Product
• Value of Marginal Product
• Law of Marginal Diminishing Product
• Production Function
• Production Possibilities Frontier
• Capital 
• Labor Theory of Value
• How the Production Function Estimates Inputs
• Factor Payment
• Economic Rent
• Cost Function
• Incremental Cost
• Marginal Input Cost  
• Fixed and Variable Costs
• Diminishing Marginal Productivity
• Costs Relate to Diminishing Marginal Productivity
• Law of Diminishing Marginal Returns
• Average Total Cost
• Average Variable Cost
• Marginal Cost
• Average Profit or Profit Margin
• Accounting Profit
• Economic Profit
• Normal Profit
• Short and Long-Run Production
• Cost Curves
• Long-Run Average Cost (LRAC)
• Production Technologies
• Economies of Scope
• Economies of Scale
• Diseconomies of Scale
• Minimum Efficient Scale
• Increasing, Constant, and Decreasing Returns to Scale
• Shape of the Average Long-Run and Short-Run Cost Curves
• Returns to Scale
• Diseconomies of Scale
• Long-Run Average Cost Curve Affect Industry Competitors
• Technology Shifts the Long-Run Average Cost Curve
• Law of Diminishing Marginal Returns