Revenue, Surplus and Deadweight Loss: Graph Areas

Match height with the correct post-change quantity.

Read Two Revenue-Area Examples

Choose the Appropriate Rectangle or Triangle

TR=P× Q. Tax revenue is tax per unit times after-tax quantity. A rectangular profit area is (P-ATC)Q. Triangle area is 1/2 bh for linear consumer surplus, producer surplus, or deadweight loss. For a triangular loss region, use the relevant vertical gap at the distorted quantity as height and the difference between distorted and efficient quantities as base. A tax triangle uses the tax wedge in the basic linear, otherwise undistorted model.

Match the Question to Its Formula

Check Sign, Scale and Units First

With other demand determinants unchanged and percentage changes measured consistently, a 10 percent price fall and 30 percent quantity rise indicate elastic demand before you divide. If an extra unit raises total cost by $12, MC cannot be $120. Direction and rough size are powerful error checks.

Label Units and Surplus Boundaries

Areas on economic graphs multiply a vertical value per unit by a horizontal number of units. Price is dollars per unit and quantity is units, so their rectangle is dollars. The same dimensional logic explains revenue, expenditure, tax revenue, profit rectangles, and surplus triangles. Label axes before calculating. Otherwise a visually correct shape can represent the wrong concept.

Consumer surplus is the area below demand and above the price paid. Producer surplus is above supply and below the price received. For straight lines and a single equilibrium, each may be triangular, but irregular or step-shaped curves require adding the actual geometric regions. Producer surplus is not always profit because fixed cost is not represented by a standard supply curve.

Separate the Tax Wedge, Revenue and Lost Trades

Before tax, 100 units trade at $20. A $4 tax reduces sales to 80. Buyers pay $22 and sellers receive $18. The wedge is $4, tax revenue is 4(80)=$320, and the basic linear deadweight loss is 1/2(4)(20)=$40. Buyers’ price rise is $2 and sellers’ received-price fall is $2, so the burden is split equally in this example.

Use ATC for Profit and Minimum AVC for Shutdown

For a competitive firm’s profit, height is P-ATC at the chosen output and width is quantity. If price is below ATC, the same rectangle represents a loss magnitude. Do not use AVC for profit. Minimum AVC supplies the standard short-run shutdown threshold when fixed costs remain unavoidable. A firm can have positive producer surplus while economic profit is negative because revenue covers variable cost and part, but not all, of fixed cost.

Separate Transfers from Lost Gains

Deadweight loss measures gains from trade that disappear, not every dollar transferred. A tax transfers revenue to government. Monopoly transfers some surplus to the producer. A binding price control may transfer surplus between buyers and sellers. DWL arises from trades not made or inefficient trades made. On a tax graph, its base is the reduction in quantity, not the remaining after-tax quantity.

Use Social Curves for Externality Losses

Externality diagrams require social curves. The welfare loss from overproduction lies between marginal social cost and marginal social benefit over the excessive units. Using private supply as the upper boundary would erase the very damage being measured.

Before accepting an area, say its unit and boundaries aloud: “dollars per unit times units,” “between demand and price,” “from efficient quantity to distorted quantity.” This short verbal check distinguishes a meaningful welfare calculation from memorized triangle hunting.

Rebuild the Formulas from Their Meaning

Cover the formulas above and rebuild, from meaning, the formulas for a marginal value, an average value, midpoint elasticity, total revenue, economic profit, marginal revenue product, tax revenue, and a deadweight-loss triangle. Beside each formula, write its unit and one condition that makes it valid. A symbol recalled without its question, unit, and condition is not yet mastered.

Check What the Shaded Region Includes

OpenStax’s surplus and efficiency section distinguishes gains to buyers and sellers from lost gains to trade. Read surplus over the units actually exchanged, with the appropriate price paid or received. A transfer between parties is not automatically a loss of total surplus.

The tax-incidence section explains how relative elasticities affect the burden. Keep the revenue rectangle over remaining transactions separate from the loss region over forgone transactions. The simple triangle calculation assumes straight-line curves and an otherwise undistorted competitive benchmark; curved boundaries require their actual area.

The externality discussion adds costs borne outside the private transaction. On a pollution graph, private supply alone does not include those external costs. Use the stated social benefit and social cost curves to identify the welfare boundary.

Calculate Revenue, Producer Surplus and Profit Separately

A hypothetical firm sells 80 units at $9 each. At that output, AVC is $6 and ATC is $11. In the basic short-run cost model, what are total revenue, producer surplus and economic profit?

Try Three Revenue-and-Surplus Area Questions

Connect Areas to the Correct Economic Model

Distinguish revenue, profit and transfers, identify social and private marginal curves, and review equilibrium and market shifts. Continue through the CLEP Microeconomics learning hub.