How firms turn inputs into outputs, why costs behave the way they do, and the crucial difference between accounting profit and economic profit
Every product you have ever bought started somewhere. Before a good or service reaches a consumer, a firm had to make decisions: what inputs to hire, how much to produce, what technology to use, and whether the revenue earned would cover the costs incurred. These decisions happen inside an organization called a firm, and understanding how firms make them is the foundation of microeconomic analysis.
Chapter 11 introduces the firm as an economic actor. We will study how firms turn inputs into outputs, how production changes as firms hire more of one input in the short run, how economists classify and measure different kinds of costs, how revenue is earned, and how profit is calculated. We will also draw a careful distinction between accounting profit, which is what businesses report on financial statements, and economic profit, which is what economists use to evaluate whether resources are being put to their best use.
This chapter prepares you for the four chapters that follow. Understanding production, costs, and profit is the necessary foundation for analyzing perfect competition, monopoly, oligopoly, and labor markets. The concepts developed here, particularly marginal cost, will reappear throughout the rest of the textbook.
Think of a business you know well — a restaurant, a shop, a service provider. What does it have to pay for no matter how busy or slow it is? What does it pay for only when it produces more? By the end of this chapter, you will be able to organize those costs precisely, calculate the cost of producing one more unit, and determine whether the business is truly earning a profit once every cost — including the owner's own time — is counted.
A firm is an organization that combines inputs to produce outputs for sale. Inputs are resources: labor, physical capital, raw materials, land, and technology. Outputs are goods and services. The firm's purpose is to transform inputs into outputs in a way that is technically feasible and, ideally, profitable.
Firms take many forms. A sole proprietorship is owned by a single person, who bears all financial risk and keeps all profit. A partnership is co-owned by two or more people. A corporation is a legal entity separate from its owners, which can raise capital by selling shares of stock. Despite these differences in legal structure, all firms face the same fundamental economic challenge: using limited resources to produce outputs at a cost that allows them to survive and operate.
Firms exist because organizing production inside a firm can be more efficient than buying and selling every input and output through separate market transactions. When a firm hires workers directly, assigns tasks, builds routines, and maintains equipment, it can reduce the costs of searching, negotiating, and contracting that would be required if every step of production were handled through individual market exchanges. Firms are organizations that internalize production rather than outsourcing it one transaction at a time.
The firm's core problem, from an economist's perspective, is this: given the prices of inputs and the technology available, what combination of inputs produces any given level of output at the lowest cost? And given those costs, what level of output maximizes profit? These questions drive every section of this chapter.
A firm is not simply a machine that produces goods automatically. It is an organization making choices under constraints, and those choices have costs, tradeoffs, and consequences just as individual choices do.
Economists classify a firm's inputs into broad categories. Understanding these categories clarifies how production works and how costs are measured.
Labor refers to human effort applied to production. It includes factory workers, software engineers, teachers, delivery drivers, managers, and everyone else whose time and skill the firm uses. Labor is usually paid in wages or salaries.
Physical capital refers to produced goods used in further production: machinery, equipment, buildings, tools, computers, and vehicles. Physical capital is distinct from financial capital, which refers to money and financial assets. When economists say "capital" in the context of production, they usually mean physical capital.
Land and natural resources include the physical space on which production takes place and the raw materials drawn from the natural world: oil, timber, minerals, water, and agricultural land.
Entrepreneurship and management refer to the human capacity to organize, direct, take risks, and innovate. Some economists list entrepreneurship as a separate factor of production alongside labor, capital, and land.
Technology is the knowledge of how to combine inputs to produce outputs. Technology is not just machines; it is the state of knowledge about production methods. Better technology means producing more output from the same inputs, or producing the same output with fewer inputs.
The output of a firm is whatever it produces: cars, loaves of bread, accounting services, software, medical diagnoses, or electricity. Output can be measured in physical units (cars per week, kilowatt-hours per year) or in dollar value, depending on the context.
The relationship between inputs and outputs is summarized by the firm's production function: a description of the maximum output that can be produced from any given combination of inputs, given available technology. The production function is a technical constraint. It describes what is physically possible, not what is economically optimal. Choosing the optimal level of output requires bringing in cost and revenue information.
| Input Category | Description | Example |
|---|---|---|
| Labor | Human effort applied to production | Factory workers, engineers, managers |
| Physical capital | Produced goods used in further production | Machinery, buildings, computers, vehicles |
| Land & natural resources | Physical space and raw materials from nature | Farmland, timber, oil, water |
| Entrepreneurship | Capacity to organize, direct, take risk, and innovate | A founder launching and managing a venture |
| Technology | Knowledge of how to combine inputs to produce outputs | Production methods, software, techniques |
Economists distinguish between two time horizons in production: the short run and the long run. These terms do not refer to specific calendar periods. They refer to the flexibility firms have to adjust their inputs.
The short run is a period in which at least one input is fixed. The firm cannot quickly change its quantity of that input, no matter what happens to output. The most common example of a fixed input is physical capital: a bakery cannot double its number of ovens within a week, even if sales suddenly surge.
The long run is a period in which all inputs can be varied. In the long run, a firm can build a new factory, install more equipment, expand its workforce, or shut down entirely.
The distinction matters because costs behave differently over different time horizons. In the short run, some costs cannot be avoided no matter what the firm produces. In the long run, all costs are variable because the firm can adjust all of its inputs.
For the analysis in this chapter, we will focus on short-run production. We will assume the firm has one fixed input (capital) and one variable input (labor). This simplification captures the essential logic of short-run production without requiring complex mathematics.
Consider a small furniture workshop. It has a fixed number of woodworking machines (capital). As the owner hires more workers (labor), output changes. The question is: how does output change as more labor is added to a fixed amount of capital?
Ask yourself: can the firm change this input right now, given the situation it is in? If the answer is no — it is locked in — that input is fixed, and you are in the short run with respect to that input. If the firm could change every input it uses, you are reasoning about the long run.
Total product (TP) is the total quantity of output a firm produces from a given combination of inputs. In our short-run framework with fixed capital and variable labor, total product is the quantity of output produced as more workers are hired.
Marginal product of labor (MPL) is the additional output produced by hiring one more worker, holding all other inputs constant.
Marginal product of labor = Change in total product ÷ Change in quantity of labor
Consider a hypothetical example. A sandwich shop has two preparation stations (fixed capital). The table below shows how output changes as workers are added.
| Workers (L) | Total Product (sandwiches/day) | Marginal Product of Labor |
|---|---|---|
| 0 | 0 | — |
| 1 | 40 | 40 |
| 2 | 90 | 50 |
| 3 | 130 | 40 |
| 4 | 160 | 30 |
| 5 | 180 | 20 |
| 6 | 190 | 10 |
| 7 | 185 | −5 |
Notice the pattern. As the first few workers are hired, output rises quickly. Two workers together produce more than twice what one worker produces, because they can specialize: one prepares ingredients while the other assembles and wraps. Marginal product rises from 40 to 50 between the first and second worker.
After the second worker, marginal product begins to fall. The third worker adds 40 sandwiches, the fourth adds 30, the fifth adds 20. By the seventh worker, marginal product is negative: the shop is so crowded that adding another worker actually reduces output.
This pattern illustrates the law of diminishing marginal returns: as a firm adds more units of a variable input (labor) to a fixed input (capital), marginal product will eventually decline.
The word "eventually" is important. Marginal product may initially rise, as specialization benefits appear. But once the fixed input becomes the binding constraint, additional variable inputs produce less and less additional output. Workers begin crowding each other out, competing for limited workspace, equipment, and coordination.
The law of diminishing marginal returns applies only in the short run, because it depends on at least one input being fixed. In the long run, the firm can increase capital as well, and the constraint loosens. Diminishing marginal returns do not mean the firm has done something wrong — they describe what happens whenever a fixed input limits how much benefit each additional variable input can add.
Diminishing marginal returns are the reason costs eventually rise as output expands in the short run. If each additional worker adds less output than the one before, the firm must hire more workers to produce each additional unit of output. That means the cost of producing each additional unit rises. This relationship between diminishing returns and rising marginal costs is developed fully in sections 11.6 and 11.7.
A firm's costs fall into two categories based on how they respond to changes in output.
Fixed costs (FC) are costs that do not change as the firm changes its level of output in the short run. Fixed costs must be paid even if the firm produces nothing. Examples include rent on a factory building, the monthly payment on a piece of equipment, property insurance premiums, and the salary of a manager on a fixed contract. Fixed costs are sometimes called overhead.
Variable costs (VC) are costs that change as output changes. When a firm produces more, it typically uses more raw materials, hires more hourly workers, and consumes more electricity. These costs rise with output. When output falls, variable costs fall too. Examples include wages paid to hourly workers, the cost of raw materials, packaging, and utilities that scale with production volume.
Total cost (TC) is the sum of fixed costs and variable costs at any given level of output.
Total cost = Fixed cost + Variable cost
TC = FC + VC
Consider a small candle-making business. Suppose fixed costs (rent, equipment payments) are $500 per month regardless of output. Variable costs depend on how many candles are produced.
| Output (candles/month) | Fixed Cost ($) | Variable Cost ($) | Total Cost ($) |
|---|---|---|---|
| 0 | 500 | 0 | 500 |
| 100 | 500 | 200 | 700 |
| 200 | 500 | 350 | 850 |
| 300 | 500 | 450 | 950 |
| 400 | 500 | 620 | 1,120 |
| 500 | 500 | 850 | 1,350 |
Notice that fixed cost stays at $500 across all output levels, including zero. Variable cost starts at zero and increases as production expands, but not at a constant rate: the pattern of variable cost reflects the pattern of marginal returns.
When total cost is graphed against output, the fixed cost appears as a horizontal line (constant regardless of output). Total cost starts above zero (at the level of fixed cost when output is zero) and rises as output increases. The shape of the total cost curve reflects variable costs. If variable costs rise slowly at first and then more steeply, the total cost curve will be relatively flat at low output and steeper at high output — a shape consistent with diminishing marginal returns.
Fixed cost and variable cost give us total cost. But firms also use several additional cost measures to make better decisions about output. The most important are average total cost and marginal cost.
Average fixed cost (AFC) is fixed cost divided by output.
AFC = FC ÷ Q
Average fixed cost falls continuously as output rises, because the same fixed cost is being spread over more and more units. This is sometimes called "spreading overhead." A factory that pays $10,000 per month in rent and produces 100 units has an AFC of $100 per unit. If it produces 1,000 units, AFC falls to $10 per unit. The fixed cost is the same; it is simply divided among more units.
Average variable cost (AVC) is variable cost divided by output.
AVC = VC ÷ Q
Average variable cost typically falls at first (as specialization and efficiency improve) and then rises (as diminishing marginal returns set in). Its shape mirrors the pattern of marginal product.
Average total cost (ATC) is total cost divided by output.
ATC = TC ÷ Q
ATC = AFC + AVC
Average total cost tells us the cost per unit of output at any given production level. It is sometimes called unit cost. Business managers often focus on ATC when deciding whether a product is profitable: if the price they can charge exceeds ATC, they are making a profit per unit; if price falls below ATC, they are losing money per unit.
Marginal cost (MC) is the additional cost of producing one more unit of output.
MC = ΔTC ÷ ΔQ
Since fixed costs do not change when output changes, marginal cost is driven entirely by changes in variable cost: MC = ΔVC ÷ ΔQ
Marginal cost is one of the most important concepts in economics. Firms use marginal cost to make production decisions: should we produce one more unit? If the revenue from that unit exceeds the marginal cost of producing it, output should expand. If marginal cost exceeds revenue, the firm should not produce that unit.
Return to the candle example and calculate marginal and average costs:
| Output (Q) | FC ($) | VC ($) | TC ($) | MC ($/unit) | ATC ($/unit) | AVC ($/unit) | AFC ($/unit) |
|---|---|---|---|---|---|---|---|
| 0 | 500 | 0 | 500 | — | — | — | — |
| 100 | 500 | 200 | 700 | 2.00 | 7.00 | 2.00 | 5.00 |
| 200 | 500 | 350 | 850 | 1.50 | 4.25 | 1.75 | 2.50 |
| 300 | 500 | 450 | 950 | 1.00 | 3.17 | 1.50 | 1.67 |
| 400 | 500 | 620 | 1,120 | 1.70 | 2.80 | 1.55 | 1.25 |
| 500 | 500 | 850 | 1,350 | 2.30 | 2.70 | 1.70 | 1.00 |
The typical shape of marginal cost: Marginal cost usually falls at first (because each additional worker initially adds more output than the last, making each additional unit cheaper to produce) and then rises (because of diminishing marginal returns). The point at which marginal cost begins to rise is the same point at which marginal product begins to fall. These are two ways of describing the same underlying phenomenon.
Whenever MC is below ATC, ATC is falling. Whenever MC is above ATC, ATC is rising. MC crosses ATC at its lowest point. This is not a coincidence; it is an algebraic necessity. Think of it like a student's grade average: if each new grade (marginal) is below the average, the average falls; if each new grade is above the average, the average rises. The minimum point of ATC is called the efficient scale of the firm.
Cost is only half of the profit calculation. A firm also earns revenue from selling its output.
Total revenue (TR) is the total amount a firm receives from selling its output. It is calculated as price multiplied by quantity sold.
TR = P × Q
If a bookstore sells 200 books at $15 each, total revenue is $3,000.
Average revenue (AR) is total revenue divided by the quantity sold.
AR = TR ÷ Q = P
For a firm selling all units at the same price, average revenue equals price. If the bookstore sells every book at $15, average revenue per book is $15.
Marginal revenue (MR) is the additional revenue earned by selling one more unit of output.
MR = ΔTR ÷ ΔQ
For a firm that sells all units at the same fixed price, marginal revenue equals price. If the bookstore can sell an additional book for $15 without changing the price of the others, its marginal revenue from that book is $15.
This is an important special case: in perfect competition, firms take the market price as given, so MR = P = AR. In markets with market power — monopoly, oligopoly — the relationship between MR and P is more complex and will be addressed in Chapters 13 and 14.
Revenue is not profit. A firm with high revenue can still lose money if its costs are even higher. The relationship between revenue and cost determines profit, which we now examine.
Profit is the difference between total revenue and total cost.
π = TR − TC
(Economists often use the Greek letter π, "pi," to denote profit. This is unrelated to the mathematical constant 3.14159.)
When TR > TC, the firm earns a positive profit (also called an economic surplus). When TR < TC, the firm incurs a loss (negative profit). When TR = TC exactly, the firm earns zero profit, which is a special case we will revisit in Chapter 12.
Using our candle example, suppose the firm can sell candles at $3.00 each.
| Output (Q) | TR ($) | TC ($) | Profit ($) |
|---|---|---|---|
| 0 | 0 | 500 | −500 |
| 100 | 300 | 700 | −400 |
| 200 | 600 | 850 | −250 |
| 300 | 900 | 950 | −50 |
| 400 | 1,200 | 1,120 | +80 |
| 500 | 1,500 | 1,350 | +150 |
At low output levels, total cost exceeds total revenue and the firm loses money. At 400 units, the firm begins to earn positive profit. At 500 units, profit is $150. The firm would continue to ask: is there an even higher output where profit is greater? It should keep expanding as long as the additional revenue from one more unit (marginal revenue) exceeds the additional cost (marginal cost).
A firm increases profit by expanding output whenever MR > MC and by reducing output whenever MR < MC. Profit is maximized when MR = MC. This rule will be used extensively in Chapters 12, 13, and 14 to study firm behavior under different market structures. If producing one more unit adds more to revenue than to cost, producing it increases profit. If one more unit costs more than it earns, it reduces profit. The sweet spot is where the two are exactly equal.
One of the most important distinctions in this chapter is between accounting profit and economic profit. They are calculated differently and answer different questions.
Accounting profit is the conventional measure of profit used in business and in financial statements. It is calculated as total revenue minus explicit costs.
Explicit costs are direct, out-of-pocket payments a firm makes for inputs: wages paid to employees, rent paid to a landlord, payments to suppliers for materials, and insurance premiums. These are costs that appear in bank records and accounting ledgers.
Accounting profit = Total revenue − Explicit costs
A restaurant that earns $300,000 in revenue and pays $250,000 in wages, rent, food, and utilities has an accounting profit of $50,000. This is the number that appears on a profit-and-loss statement and the number used for income tax purposes.
Economic profit is a broader concept. It subtracts both explicit costs and implicit costs from total revenue.
Implicit costs are the opportunity costs of inputs the firm uses but does not pay for directly. The most important implicit cost for many small businesses is the opportunity cost of the owner's own time and capital.
Consider the restaurant owner who works 60 hours a week in her restaurant. If she did not own the restaurant, she could earn $70,000 per year as a manager elsewhere. That $70,000 is an implicit cost of running her restaurant: it is the earnings she forgoes by choosing to be a restaurant owner.
Similarly, if the owner invested $200,000 of her own savings into the restaurant, she cannot simultaneously invest that money in a bond or stock portfolio. If she could earn a 5% return elsewhere (let's say $10,000 per year), that foregone return is also an implicit cost.
Economic profit = Total revenue − Explicit costs − Implicit costs
Economic profit = Accounting profit − Implicit costs
When economic profit equals zero, the firm earns exactly enough revenue to cover both explicit and implicit costs, including a fair return on the owner's time and capital. This situation is called normal profit or zero economic profit.
Normal profit is not a failure. It means the firm is covering all of its costs, including the opportunity cost of the owner's resources. The owner is doing exactly as well in this business as they would in their next best alternative. There is no incentive to exit the industry.
This concept is important for understanding competitive markets and long-run equilibrium in Chapter 12, where we will see that in a competitive market, entry and exit drive economic profit toward zero in the long run, while firms continue to earn normal profits.
| Concept | What is Subtracted | What it Measures |
|---|---|---|
| Accounting profit | Explicit costs only | Business financial performance |
| Economic profit | Explicit + implicit costs | Whether resources are in their best use |
| Normal profit | Economic profit = 0 | Resources earning their opportunity cost |
Economists use economic profit to evaluate resource allocation. Accounting profit is used for tax purposes, investor reporting, and business management. A firm can be profitable by accounting standards and still allocate resources inefficiently from an economic perspective.
The models developed in this chapter are simplifications. Real firms face more complexity: multiple products, many types of labor, dozens of suppliers, multiple locations, and uncertainty about future prices and demand. Nevertheless, the principles developed here apply across this complexity.
Firms monitor costs obsessively. Whether a firm is a local bakery or a multinational corporation, understanding cost structure is fundamental to survival and strategy. The distinction between fixed and variable costs determines how a firm responds to downturns: a firm with high fixed costs and low variable costs cannot cut costs quickly when demand falls.
Marginal thinking drives output decisions. Firms that push output beyond the point where MR = MC destroy value. A factory adding a night shift when the marginal cost of the additional production exceeds the price received is making a loss on those units. Understanding marginal cost prevents this error.
Economic profit guides long-run investment decisions. If a business consistently earns negative economic profit (even if it shows accounting profit), it will eventually lose owners to better opportunities. Over time, industries that earn negative economic profit shrink as owners exit. Industries with positive economic profit attract new entrants. This dynamic — the movement of resources toward their best uses — is one of the fundamental mechanisms through which market economies coordinate production.
The short run and long run interact. In the short run, a firm might continue operating even at a loss, provided it can cover its variable costs (we will examine this shutdown decision in Chapter 12). But in the long run, a firm must cover all of its costs, including implicit costs. Distinguishing short-run from long-run thinking helps firms avoid both premature shutdowns and the trap of staying in a losing enterprise indefinitely.
Technology shifts cost curves. When a firm adopts a new technology, it may be able to produce the same output at lower cost, shifting its cost curves downward. Technological change is one of the key forces that allows firms to offer lower prices while remaining profitable, which benefits consumers and supports economic growth.
Plot workers (L) on the horizontal axis and total product (TP) on the vertical axis. The curve starts at the origin (zero workers produce zero output) and rises with a shape that increases steeply at first, flattens, and may decline slightly at very high labor inputs. Label the region where the curve rises at an increasing rate (increasing marginal returns), the region where it rises at a decreasing rate (diminishing marginal returns), and, if present, the region where it falls (negative marginal returns).
Practice: Using the sandwich shop data from section 11.4, plot the total product curve. At what labor input does marginal product begin to fall?
Plot workers on the horizontal axis and marginal product on the vertical axis. Marginal product rises at first, peaks, then falls, eventually crossing the horizontal axis when total product reaches its maximum. The peak of the MP curve corresponds to the inflection point on the TP curve.
Practice: At what number of workers does marginal product peak in the sandwich shop example? What law explains the subsequent decline?
Plot output (Q) on the horizontal axis and cost (in dollars) on the vertical axis. Fixed cost (FC) is a horizontal line above the axis, constant at all output levels. Variable cost (VC) starts at zero and rises; relatively flat at first, then steeper at higher output due to diminishing marginal returns. Total cost (TC) starts at the FC level (not zero) and rises in the same shape as VC, shifted upward by the constant amount of FC.
Practice: Why does the total cost curve start above zero even when output is zero?
Plot output on the horizontal axis and cost per unit on the vertical axis. AFC is a downward-sloping curve approaching but never reaching the horizontal axis. AVC is U-shaped, falling then rising. ATC is U-shaped above AVC, with the vertical gap narrowing as output increases (since AFC shrinks). MC is U-shaped, starting below AVC, falling, reaching a minimum, then rising, and crossing both AVC and ATC at their lowest points.
Practice: Why does the MC curve intersect the ATC curve exactly at ATC's minimum point? Explain using the logic of how a marginal value affects an average.
Worked Data Table: Cost Calculations — A small pottery studio has the following cost data for a month. Fixed costs are $400. Fill in the missing values for MC, AFC, AVC, and ATC.
| Output (Q) | FC ($) | VC ($) | TC ($) | MC ($/unit) | AFC ($/unit) | AVC ($/unit) | ATC ($/unit) |
|---|---|---|---|---|---|---|---|
| 0 | 400 | 0 | 400 | — | — | — | — |
| 10 | 400 | 100 | 500 | ? | ? | ? | ? |
| 20 | 400 | 180 | 580 | ? | ? | ? | ? |
| 30 | 400 | 240 | 640 | ? | ? | ? | ? |
| 40 | 400 | 340 | 740 | ? | ? | ? | ? |
| 50 | 400 | 490 | 890 | ? | ? | ? | ? |
MC between 0 and 10 units: (500 − 400) ÷ 10 = $10.00 per unit. MC between 10 and 20 units: (580 − 500) ÷ 10 = $8.00 per unit. ATC at Q = 30: 640 ÷ 30 ≈ $21.33 per unit. AFC at Q = 50: 400 ÷ 50 = $8.00 per unit.
Identify and explain the error in each of the following statements.
Chapter 11 gave you the tools to understand how firms produce, how their costs behave, and how profit — both accounting and economic — is calculated. Chapter 12 puts these tools to work. It introduces perfect competition, the market structure in which many firms sell identical products and no single firm has the power to set a price. In perfect competition, firms are price takers: the price is determined by the market, and each firm accepts it as given. Using the cost concepts from this chapter, you will analyze how a perfectly competitive firm chooses its output to maximize profit in the short run, what happens when the firm suffers a loss, when it should shut down, and how markets adjust in the long run as firms enter and exit. The tools of marginal cost and marginal revenue developed here will be applied directly in the next chapter.