Consumer surplus is closely related yo the demand curve for
a product. To see how they are related let’s continue our example and consider
the demand curve for this rare Elvis Presley album.
We begin by using the willingness to pay of the four
possible buyers to find the demand schedule for the album. The table in the
demand schedule that corresponds to table. If the price is above $100 the
quantity demanded in the market is because no buyer is willing to pay that
much. If the price between and the quantity demanded is because only John is
willing to pay such a high price. If the price is between and the quantity
demanded is because both john and Paul
are willing to pay the price. We can continue this analysis for other prices as
well. In this way the demand schedule is derived from the willingness to pay of
the four possible buyers.
The demand curve that corresponds of this demand schedule.
Note the relationship between the height of the demand curve and the buyers
willingness to pay. At any quantity the price given by the demand curve shows
the willingness to pay of the marginal buyer the buyer who would leave the
market first if the price were any higher. At a quantity of for instance the
demand curve has a height of the price that Ringo the ( the marginal buyer ) is
willing to pay for an album. At a quantity of albums the demand curve has a
height of the price that George ( who is now the marginal buyer) is willing to pay.
Because the demand curve reflects buyers’ willingness to pay
we can also use it to measure consumer surplus. The demand curve to compute
consumer surplus in our example. In the price is ( or slightly above) and the
quantity demanded. Note that the area above the price and below the demand
curve equals. This amount is exactly the consumer surplus we computed earlier
when only album is sold.
Consumer surplus when the price is (or slightly above). In
this case the area above the price and below the demand curve equals the total
area of the two rectangles John’s consumer surplus at this price is and Paul’s.
This area equals a total. Once again this amount is the consumer surplus we
computed earlier.
The lesson from this example holds for all demand curves.
The area below the demand curve and above the price measures the consumer
surplus in a market. The reason is that
the height of the demand curve measures the value buyers place on the good as
measured by their willingness to pay for it. The difference between this
willingness to pay and the market price is each buyer’s consumer surplus. Thus
the total area below the demand curve and above the price is the sum of the
consumer surplus of all buyers in the market for a good or service.
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