# Average cost

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In economics, average cost or unit cost is equal to total cost (TC) divided by the number of units of a good produced (the output Q):

## Contents

${\displaystyle AC={\frac {TC}{Q}}.}$

It is also equal to the sum of average variable costs (total variable costs divided by Q) and average fixed costs (total fixed costs divided by Q). Average costs may be dependent on the time period considered (increasing production may be expensive or impossible number in the short term, for example). Average costs affect the supply curve and are a fundamental component of supply and demand.

## Short-run average cost

Short-run costs are those that vary with almost no time lagging. Labor cost and the cost of raw materials are short-run costs, but physical capital is not.

An average cost curve can be plotted with cost on the vertical axis and quantity on the horizontal axis. Marginal costs are often also shown on these graphs, with marginal cost representing the cost of the last unit produced at each point; marginal costs in the short run are the slope of the variable cost curve (and hence the first derivative of variable cost).

A typical average cost curve has a U-shape, because fixed costs are all incurred before any production takes place and marginal costs are typically increasing, because of diminishing marginal productivity. In this "typical" case, for low levels of production marginal costs are below average costs, so average costs are decreasing as quantity increases. An increasing marginal cost curve intersects a U-shaped average cost curve at the latter's minimum, after which the average cost curve begins to slope upward. For further increases in production beyond this minimum, marginal cost is above average costs, so average costs are increasing as quantity increases. For example: for a factory designed to produce a specific quantity of widgets per period—below a certain production level, average cost is higher due to under-used equipment, and above that level, production bottlenecks increase average cost.

## Long-run average cost

Long-run average cost is the unit cost of producing a certain output when all inputs, even physical capital, are variable. The behavioral assumption is that the firm will choose that combination of inputs that produce the desired quantity at the lowest possible cost.

A long-run average cost curve is typically downward sloping at relatively low levels of output, and upward or downward sloping at relatively high levels of output. Most commonly, the long-run average cost curve is U-shaped, by definition reflecting economies of scale where negatively sloped and diseconomies of scale where positively sloped.

If the firm is a perfect competitor in all input markets, and thus the per-unit prices of all its inputs are unaffected by how much of the inputs the firm purchases, then it can be shown [1] [2] [3] that at a particular level of output, the firm has economies of scale (i.e., is operating in a downward sloping region of the long-run average cost curve) if and only if it has increasing returns to scale, the latter being exclusively a feature of the production function. Likewise, it has diseconomies of scale (is operating in an upward sloping region of the long-run average cost curve) if and only if it has decreasing returns to scale, and has neither economies nor diseconomies of scale if it has constant returns to scale. With perfect competition in the output market the long-run market equilibrium will involve all firms operating at the minimum point of their long-run average cost curves (i.e., at the borderline between economies and diseconomies of scale).

If, however, the firm is not a perfect competitor in the input markets, then the above conclusions are modified. For example, if there are increasing returns to scale in some range of output levels, but the firm is so big in one or more input markets that increasing its purchases of an input drives up the input's per-unit cost, then the firm could have diseconomies of scale in that range of output levels. Conversely, if the firm is able to get bulk discounts of an input, then it could have economies of scale in some range of output levels even if it has decreasing returns in production in that output range.

In some industries, long-run average cost is always declining (economies of scale exist indefinitely). This means that the largest firm tends to have a cost advantage, and the industry tends naturally to become a monopoly, and hence is called a natural monopoly. Natural monopolies tend to exist in industries with high capital costs in relation to variable costs, such as water supply and electricity supply.

## Relationship to marginal cost

When average cost is declining as output increases, marginal cost is less than average cost. When average cost is rising, marginal cost is greater than average cost. When average cost is neither rising nor falling (at a minimum or maximum), marginal cost equals average cost.

Other special cases for average cost and marginal cost appear frequently:

• Constant marginal cost/high fixed costs: each additional unit of production is produced at constant additional expense per unit. The average cost curve slopes down continuously, approaching marginal cost. An example is hydroelectric generation, which has no fuel expense, limited maintenance expenses and a high up-front fixed cost (ignoring irregular maintenance costs or useful lifespan). Industries with fixed marginal costs, such as electrical transmission networks, may meet the conditions for a natural monopoly, because once capacity is built, the marginal cost to the incumbent of serving an additional customer is always lower than the average cost for a potential competitor. The high fixed capital costs are a barrier to entry.
• Two popular pricing mechanisms are average cost pricing (or rate of return regulation) and marginal cost pricing. A monopoly produces where its average cost curve meets the market demand curve under average cost pricing, referred to as the average cost pricing equilibrium.
• Minimum efficient scale: Marginal or average costs may be nonlinear, or have discontinuities. Average cost curves may therefore only be shown over a limited scale of production for a given technology. For example, a nuclear plant would be extremely inefficient (high average cost) for production in small quantities. Similarly, its maximum output for any given time period may essentially be fixed, and production above that level may be technically impossible, dangerous or extremely costly. The long run elasticity of supply are higher, as new plants could be built and brought on-line.
• Zero fixed costs (long-run analysis) and constant marginal cost: since there are no economies of scale, average cost is equal to the constant marginal cost.

## Relationship between AC, AFC, AVC and MC

1. The Average Fixed Cost curve (AFC) starts from a height and goes on declining continuously as production increases.

2. The Average Variable Cost curve, Average Cost curve and the Marginal Cost curve start from a height, reach the minimum points, then rise sharply and continuously.

3. The Average Fixed Cost curve approaches zero asymptotically. The Average Variable Cost curve is never parallel to or as high as the Average Cost curve due to the existence of positive Average Fixed Costs at all levels of production; but the Average Variable Cost curve asymptotically approaches the Average Cost curve from below.

4. The Marginal Cost curve always passes through the minimum points of the Average Variable Cost and Average Cost curves, though the Average Variable Cost curve attains the minimum point prior to that of the Average Cost curve.

## Related Research Articles

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In economics, profit maximization is the short run or long run process by which a firm may determine the price, input, and output levels that lead to the highest profit. Neoclassical economics, currently the mainstream approach to microeconomics, usually models the firm as maximizing profit.

The following outline is provided as an overview of and topical guide to industrial organization:

In economics, marginal cost is the change in the total cost that arises when the quantity produced is incremented by one unit; that is, it is the cost of producing one more unit of a good. Intuitively, marginal cost at each level of production includes the cost of any additional inputs required to produce the next unit. At each level of production and time period being considered, marginal costs include all costs that vary with the level of production, whereas other costs that do not vary with production are fixed and thus have no marginal cost. For example, the marginal cost of producing an automobile will generally include the costs of labor and parts needed for the additional automobile but not the fixed costs of the factory that have already been incurred. In practice, marginal analysis is segregated into short and long-run cases, so that, over the long run, all costs become marginal. Where there are economies of scale, prices set at marginal cost will fail to cover total costs, thus requiring a subsidy. Marginal cost pricing is not a matter of merely lowering the general level of prices with the aid of a subsidy; with or without subsidy it calls for a drastic restructuring of pricing practices, with opportunities for very substantial improvements in efficiency at critical points.

A production–possibility frontier (PPF), production possibility curve (PPC), or production possibility boundary (PPB), or Transformation curve/boundary/frontier is a curve which shows various combinations of the amounts of two goods which can be produced within the given resources and technology/a graphical representation showing all the possible options of output for two products that can be produced using all factors of production, where the given resources are fully and efficiently utilized per unit time. A PPF illustrates several economic concepts, such as allocative efficiency, economies of scale, opportunity cost, productive efficiency, and scarcity of resources.

In economics, a production function gives the technological relation between quantities of physical inputs and quantities of output of goods. The production function is one of the key concepts of mainstream neoclassical theories, used to define marginal product and to distinguish allocative efficiency, a key focus of economics. One important purpose of the production function is to address allocative efficiency in the use of factor inputs in production and the resulting distribution of income to those factors, while abstracting away from the technological problems of achieving technical efficiency, as an engineer or professional manager might understand it.

In economics and in particular neoclassical economics, the marginal product or marginal physical productivity of an input is the change in output resulting from employing one more unit of a particular input, assuming that the quantities of other inputs are kept constant.

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In economics, returns to scale describe what happens to long run returns as the scale of production increases, when all input levels including physical capital usage are variable. The concept of returns to scale arises in the context of a firm's production function. It explains the long run linkage of the rate of increase in output (production) relative to associated increases in the inputs. In the long run, all factors of production are variable and subject to change in response to a given increase in production scale. While economies of scale show the effect of an increased output level on unit costs, returns to scale focus only on the relation between input and output quantities.

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In economics, a cost curve is a graph of the costs of production as a function of total quantity produced. In a free market economy, productively efficient firms optimize their production process by minimizing cost consistent with each possible level of production, and the result is a cost curve. Profit-maximizing firms use cost curves to decide output quantities. There are various types of cost curves, all related to each other, including total and average cost curves; marginal cost curves, which are equal to the differential of the total cost curves; and variable cost curves. Some are applicable to the short run, others to the long run.

In economics, total cost (TC) is the total economic cost of production and is made up of variable cost, which varies according to the quantity of a good produced and includes inputs such as labor and raw materials, plus fixed cost, which is independent of the quantity of a good produced and includes inputs that cannot be varied in the short term: fixed costs such as buildings and machinery, including sunk costs if any.

In economics the long run is a theoretical concept in which all markets are in equilibrium, and all prices and quantities have fully adjusted and are in equilibrium. The long run contrasts with the short run, in which there are some constraints and markets are not fully in equilibrium.

In economics, supply is the amount of a resource that firms, producers, labourers, providers of financial assets, or other economic agents are willing and able to provide to the marketplace or directly to another agent in the marketplace. Supply can be in currency, time, raw materials, or any other scarce or valuable object that can be provided to another agent. This is often fairly abstract. For example in the case of time, supply is not transferred to one agent from another, but one agent may offer some other resource in exchange for the first spending time doing something. Supply is often plotted graphically as a supply curve, with the quantity provided plotted horizontally and the price plotted vertically.

In industrial organization, the minimum efficient scale (MES) or efficient scale of production is the lowest point where the plant can produce such that its long run average costs are minimized. It is also the point at which the firm can achieve necessary economies of scale for it to compete effectively within the market.

A firm will choose to implement a shutdown of production when the revenue received from the sale of the goods or services produced cannot even cover the variable costs of production. In that situation, the firm will experience a higher loss when it produces, compared to not producing at all.

In economics, the marginal product of labor (MPL) is the change in output that results from employing an added unit of labor. It is a feature of the production function, and depends on the amounts of physical capital and labor already in use.

The socially optimal firm size is the size for a company in a given industry at a given time which results in the lowest production costs per unit of output.

## References

1. Gelles, Gregory M., and Mitchell, Douglas W., "Returns to scale and economies of scale: Further observations," Journal of Economic Education 27, Summer 1996, 259-261.
2. Frisch, R., Theory of Production, Dordrecht: D. Reidel, 1965.
3. Ferguson, C. E., The Neoclassical Theory of Production and Distribution, London: Cambridge University Press, 1969.