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For other uses, see Demand (disambiguation).

In economics, demand is the utility for a good or service of an economic agent, relative to his/her income. (Note: This distinguishes “demand” from “quantity demanded”, where demand is a listing or graphing of quantity demanded at each possible price. In contrast to demand, quantity demanded is the exact quantity demanded at a certain price. Changing the actual price will change the quantity demanded, but it will not change the demand, because demand is a listing of quantities that would be bought at various prices, not just the actual price.)

Demand is a buyer's willingness and ability to pay a price for a specific quantity of a good or service. Demand refers to how much (quantity) of a product or service is desired by buyers at various prices. The quantity demanded is the amount of a product people are willing to buy at a certain price; the relationship between price and quantity demanded is known as the demand.[1] (see also supply and demand). The term demand signifies the ability or the willingness to buy a particular commodity at a given point of time, ceteris paribus.

Inverse demand function[edit]

In its standard form a linear demand equation is Q = a - bP. That is, quantity demanded is a function of price. The inverse demand equation, or price equation, treats price as a function g of quantity demanded: P = f(Q). To compute the inverse demand equation, simply solve for P from the demand equation.[2] For example, if the demand equation is Q = 240 - 2P then the inverse demand equation would be P = 120 - .5Q, the right side of which is the inverse demand function.[3]

The inverse demand function is useful in deriving the total and marginal revenue functions. Total revenue equals price, P, times quantity, Q, or TR = P×Q. Multiply the inverse demand function by Q to derive the total revenue function: TR = (120 - .5Q) × Q = 120Q - 0.5Q². The marginal revenue function is the first derivative of the total revenue function; here MR = 120 - Q. Note that the MR function has the same y-intercept as the inverse demand function in this linear example; the x-intercept of the MR function is one-half the value of that of the demand function, and the slope of the MR function is twice that of the inverse demand function. This relationship holds true for all linear demand equations. The importance of being able to quickly calculate MR is that the profit-maximizing condition for firms regardless of market structure is to produce where marginal revenue equals marginal cost (MC). To derive MC the first derivative of the total cost function is taken. For example assume cost, C, equals 420 + 60Q + Q2. Then MC = 60 + 2Q. Equating MR to MC and solving for Q gives Q = 20. So 20 is the profit maximizing quantity: to find the profit-maximizing price simply plug the value of Q into the inverse demand equation and solve for P.

Residual demand curve[edit]

The demand curve facing a particular firm is called the residual demand curve. The residual demand curve is the market demand that is not met by other firms in the industry at a given price. The residual demand curve is the market demand curve D(p), minus the supply of other organizations, So(p): Dr(p) = D(p) - So(p )[4]

Is the demand curve for PC firm really flat?[edit]

Practically every introductory microeconomics text describes the demand curve facing a perfectly competitive firm as being flat or horizontal. A horizontal demand curve is perfectly elastic. If there are n identical firms in the market then the elasticity of demand PED facing any one firm is

PEDmi = nPEDm - (n - 1) PES[4]

where PEDm is the market elasticity of demand, PES is the elasticity of supply of each of the other firms, and (n -1) is the number of other firms.[5] This formula suggests two things. The demand curve is not perfectly elastic and if there are a large number of firms in the industry the elasticity of demand for any individual firm will be extremely high and the demand curve facing the firm will be nearly flat.[6]

For example assume that there are 80 firms in the industry and that the demand elasticity for industry is -1.0 and the price elasticity of supply is 3. Then

PEDmi = nPEDm - (n - 1) PES,
PEDmi = (-1) - (80 - 1) 3,
PEDmi = -1(80) - (79 x 3)
PEDmi = -80 - 237 = - 317

That is the firm PED is 317 times as elastic as the market PED. If a firm raised its price “by one tenth of one percent demand would drop by nearly one third.”[7] if the firm raised its price by three tenths of one percent the quantity demanded would drop by nearly 100%. Three tenths of one percent marks the effective range of pricing power the firm has because any attempt to raise prices by a higher percentage will effectively reduce quantity demanded to zero.

Demand management in economics[edit]

Demand management in economics is the art or science of controlling economic or aggregate demand to avoid a recession. Such management is inspired by Keynesian macroeconomics, and Keynesian economics is sometimes referred to as demand-side economics.


  1. ^ Sullivan, Arthur; Steven M. Sheffrin (2003). Economics: Principles in action. Upper Saddle River, New Jersey 07458: Pearson Prentice Hall. p. 79. ISBN 0-13-063085-3. 
  2. ^ The form of the inverse linear demand equation is P = a/b - 1/bQ.
  3. ^ Samuelson, W & Marks, S. Managerial Economics 4th ed. p. 37. Wiley 2003.
  4. ^ a b Perloff (2008) p. 243.
  5. ^ Perloff (2008) p. 245–246
  6. ^ Perloff (2008) p. 244.
  7. ^ Prloff (2008) p. 243.