Chapter 7: Consumers, Producers & the Efficiency of Markets

How free markets create value — and what happens when they don't

Running Example

The Strawberry Market

To make these ideas concrete, we'll return to the same market all chapter: strawberries. Buyers have a willingness to pay that falls as they get more; sellers have a cost that rises as they produce more. Two straight lines capture all of that.

Demand: P = 30 − 2Q what buyers will pay
Supply: P = 10 + 2Q what sellers need
Equilibrium: Q* = 5,  P* = $20 where both lines cross

Setting demand equal to supply gives us the equilibrium: 5 pints at $20 each. Everything else in Chapter 7 follows from understanding what happens around that crossing point.

Section 1

What Buyers Gain: Consumer Surplus

Suppose you'd pay up to $28 for a pint of strawberries, but the market price is $20. You "saved" $8 — that saving is your consumer surplus. Across all buyers, CS is the total area between the demand curve and the market price.

Because demand is a straight line, that area is always a triangle. At equilibrium the base runs from Q=0 to Q=5, and the height is $30 − $20 = $10, giving CS = ½ × 5 × 10 = $25.

CS = area above price, below demand curve = ½ × Q* × (Pmax − P*)

Section 2

What Sellers Gain: Producer Surplus

Sellers also gain. A farmer whose cost to grow a pint is $12 earns $8 in profit when the market price is $20. Producer surplus is the total area between the market price and the supply curve — the extra revenue sellers receive above the minimum they'd accept.

At equilibrium the PS triangle has base Q=5 and height $20 − $10 = $10, so PS = ½ × 5 × 10 = $25. Total surplus = CS + PS = $50.

PS = area below price, above supply curve = ½ × Q* × (P* − Pmin)

Section 3

The Surplus Explorer

Drag the price line up or down to see how surplus redistributes between buyers and sellers, and where deadweight loss appears. Notice that total surplus is maximized at exactly $20.

Drag the price line up or down to see how surplus changes.

0 10 20 30 35 0 5 10 15 Quantity (pints) Price ($) Demand Supply P = $20.00

Surplus Values

Price $20.00
Consumer $25.00
Producer $25.00
Total $50.00
DWL $0.00

Equilibrium!

Section 4

When Government Steps In: Price Floors

Governments sometimes set a price floor — a minimum legal price — to protect sellers. The classic example is agricultural price supports. The intention is good: keep farmers in business. But a binding floor (set above equilibrium) creates a gap between quantity supplied and quantity demanded. That gap is excess supply, and the lost trades become deadweight loss.

Excess Supply 0 10 20 30 35 0 5 10 15 Qd Qs Quantity (pints) Price ($) Demand Supply Floor

Market Data

Floor Price $20.00 (free)
Q Demanded 5.00
Q Supplied 5.00
Excess Supply 0.00
Consumer $25.00
Producer $25.00
Total $50.00
DWL $0.00

Summary

Key Takeaways

  • Consumer surplus (CS) measures buyer benefit — the gap between willingness to pay and the actual price.
  • Producer surplus (PS) measures seller benefit — revenue above the minimum sellers would accept.
  • Free markets maximize total surplus (CS + PS = $50 in our model). Any price different from equilibrium shrinks the total pie.
  • Deadweight loss is the surplus that no one gets when mutually beneficial trades don't happen — pure economic waste.
  • Price floors above equilibrium cause excess supply, reduce CS, and create DWL even if they raise PS for some sellers.
  • Efficiency is not equality. A market can be perfectly efficient and still distribute income very unequally — that's a separate question.

Ready to test yourself?

Work through problems on consumer surplus, producer surplus, and deadweight loss.

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