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Economics · Microeconomics

Consumer & Producer Surplus

Measure consumer, producer, and total surplus as the triangular areas of a linear supply-and-demand market.

$
Price where quantity demanded falls to zero.
$
Lowest price at which sellers supply anything.
$
Market-clearing price where supply meets demand.
units
Units traded at the equilibrium price.
Try a scenario
Total surplus
$400.00

Consumer surplus $250.00 + producer surplus $150.00 = total surplus $400.00.

Consumer surplus
$250.00
Producer surplus
$150.00
Supply & demand — the curves cross at equilibrium; surplus is the area to each side
Falling demand line and rising supply line crossing at the equilibrium point, with consumer surplus above and producer surplus below the equilibrium price200Q = 0Q = 100
DemandSupply— they cross at equilibrium (Q = 50, $10.00).

Consumer and producer surplus are the two triangular areas between price and the demand and supply curves at equilibrium. With a demand choke price of $20, a supply intercept of $4, an equilibrium price of $10, and 50 units traded, CS = $250, PS = $150, and total surplus = $400.

What consumer and producer surplus measure

In a linear supply-and-demand market, consumer surplus is the value buyers get above what they actually pay: the gap between the highest price each buyer would accept and the market price, summed across everyone who buys. Producer surplus mirrors it for sellers — the gap between the market price and the lowest price each seller would accept. Because both curves are straight lines, each surplus is a right triangle sitting against the equilibrium price line, so the area formula ½ × base × height gives an exact answer.

CS = ½(P_dmax − P_eq)·Q_eq PS = ½(P_eq − P_smin)·Q_eq

Each surplus is a triangle: height is the price gap, base is the equilibrium quantity. Total surplus = CS + PS.

Worked example

Demand hits zero at a choke price of $20, supply starts at $4, the market clears at $10, and 50 units change hands.

  1. 1
    Find the demand choke price and equilibrium price. The choke price is where quantity demanded reaches zero — here $20. The equilibrium price is $10, so the consumer-surplus triangle is $20 − $10 = $10 tall.
  2. 2
    Compute consumer surplus. CS = ½ × (P_dmax − P_eq) × Q_eq = ½ × ($20 − $10) × 50 = $250.
  3. 3
    Find the supply intercept price. The intercept is the lowest price sellers accept — here $4. The producer-surplus triangle is $10 − $4 = $6 tall.
  4. 4
    Compute producer surplus. PS = ½ × (P_eq − P_smin) × Q_eq = ½ × ($10 − $4) × 50 = $150.
  5. 5
    Add them for total surplus. Total surplus = CS + PS = $250 + $150 = $400 — the total gains from trade at equilibrium.

What each input means

The two prices set the triangle heights; the equilibrium quantity is the shared base.

TermWhat it isRole in the formula
Demand choke price (P_dmax)The demand curve’s price intercept — the price at which quantity demanded falls to zero.Top of the consumer-surplus triangle.
Supply intercept price (P_smin)The supply curve’s price intercept — the lowest price at which sellers supply anything.Bottom of the producer-surplus triangle.
Equilibrium price (P_eq)The market-clearing price where quantity supplied equals quantity demanded.The dividing line between the two triangles.
Equilibrium quantity (Q_eq)The number of units traded at the equilibrium price.The shared base of both triangles.

Reading the result

Straight-line assumption. These formulas assume both the supply and demand curves are straight lines, so each surplus is a clean triangle. With curved (non-linear) demand or supply the shape is no longer a triangle and you would integrate the area instead — treat this calculator as the standard introductory-microeconomics model.

Total surplus is market efficiency. The sum CS + PS is the total gains from trade. A competitive market at equilibrium maximizes this total — no other quantity produces more combined value for buyers and sellers.

Deadweight loss lives off equilibrium. When output is pushed away from the equilibrium quantity — by a price ceiling, a tax, a subsidy, or monopoly pricing — some mutually beneficial trades never happen. The lost surplus is a third triangle called deadweight loss, which shrinks the total below the $400 an efficient market would reach in the example.

What is consumer surplus?
Consumer surplus is the total value buyers receive above what they pay — the gap between the most each buyer would pay and the market price, summed over everyone who buys. On a linear demand curve it is the triangle ½ × (P_dmax − P_eq) × Q_eq, which is $250 in the worked example.
What is the choke price?
The choke price is the demand curve’s price intercept — the price so high that quantity demanded falls to zero and no one buys. It sets the top of the consumer-surplus triangle; in the example it is $20.
What is producer surplus?
Producer surplus is the value sellers gain above the least they would accept — the gap between the market price and each seller’s minimum price, summed over all units sold. It is the triangle ½ × (P_eq − P_smin) × Q_eq, or $150 in the example.
Why is each surplus half the base times the height?
Because linear supply and demand curves are straight lines, each surplus is a right triangle resting on the equilibrium quantity. The area of a triangle is ½ × base × height, where the base is Q_eq and the height is the price gap.
What is total surplus and why does it matter?
Total surplus is consumer surplus plus producer surplus — the combined gains from trade. It is maximized at the competitive equilibrium, which is why economists use it as the standard measure of market efficiency.
What is deadweight loss?
Deadweight loss is the surplus destroyed when the market trades a quantity other than the equilibrium one — because of a tax, price control, or monopoly. It is the value of the mutually beneficial trades that no longer happen, so total surplus falls below its efficient maximum.

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