Price Elasticity of Demand
Why do some customers reduce purchases when prices rise, while others continue buying? Price elasticity of demand explains how strongly the quantity people buy responds to a change in price. It is useful for understanding household spending, competition, and business pricing decisions.
What Is Price Elasticity of Demand?
Price elasticity of demand measures the percentage change in the quantity demanded of a product in response to a percentage change in its price, assuming other relevant factors remain unchanged.
In simple terms, it helps explain whether customers are highly sensitive or relatively insensitive to a price change. The result depends on the product, its alternatives, customer preferences, and the time available to adjust.
Price Elasticity of Demand Formula
Price Elasticity of Demand (Ed)
Ed = % Change in Quantity Demanded ÷ % Change in Price
For a typical downward-sloping demand curve, price and quantity demanded move in opposite directions. The calculated elasticity is therefore usually negative. Many introductory economics explanations report its absolute value to classify demand as elastic or inelastic.
When comparing two ordinary price-and-quantity observations, percentage changes can be calculated using the midpoint method. This uses the average of the original and new values as the denominator and gives the same magnitude when moving between the two observations in either direction.
Understanding Price Elasticity Through Graphs
A demand curve shows how the quantity consumers want to buy changes when the price of a product changes, assuming other factors remain unchanged. Both elastic and inelastic demand curves generally slope downward from left to right.
How to read the axes
- Y-axis (vertical): shows price in rupees. Higher prices appear higher on the graph.
- X-axis (horizontal): shows quantity demanded in units. Larger quantities appear farther to the right.
- Price falls: move down the Y-axis and generally right along the demand curve as quantity demanded increases.
- Price rises: move up the Y-axis and generally left along the demand curve as quantity demanded decreases.
How to recognise elasticity
- Elastic demand: quantity demanded responds relatively strongly to a price change. It is often illustrated with a flatter curve.
- Inelastic demand: quantity demanded responds relatively weakly to a price change. It is often illustrated with a steeper curve.
- Perfectly inelastic demand: is represented by a vertical curve because quantity remains unchanged as price changes.
Relatively Elastic Demand
When price decreases, quantity demanded responds relatively strongly. This can happen when consumers have many close substitutes or can easily switch to another product.
Remember: Elastic demand means a larger percentage change in quantity demanded relative to the percentage change in price.
Relatively Inelastic Demand
When price decreases, quantity demanded responds relatively weakly. Some essential products may show this pattern over certain price ranges because consumers have fewer alternatives.
Remember: Inelastic demand means a smaller percentage change in quantity demanded relative to the percentage change in price.
The easiest way to remember the direction
Price decreases
Move down the graph and right along the demand curve: quantity demanded generally increases.
Price increases
Move up the graph and left along the demand curve: quantity demanded generally decreases.
Important: Both curves slope downward. Ordinary inelastic demand is shown as relatively steep, not perfectly vertical. A vertical demand curve represents perfectly inelastic demand, where quantity does not change as price changes.
Economics note: These graphs are illustrative, and their line coordinates are not measured economic data. Curve steepness alone does not determine elasticity at every point: elasticity depends on percentage changes in price and quantity, and the scales used on the axes. The axis values are illustrative rupee prices and quantities, not a calculated dataset.
Worked Example: Calculating Elasticity
Original Price
₹100
Original quantity demanded: 200 units
New Price
₹110
New quantity demanded: 160 units
Step 1: Calculate the Percentage Change in Price
Using the midpoint method: (110 − 100) ÷ 105 × 100 = approximately 9.52%.
Step 2: Calculate the Percentage Change in Quantity
(160 − 200) ÷ 180 × 100 = approximately −22.22%.
Step 3: Calculate Elasticity
Ed = −22.22% ÷ 9.52% ≈ −2.33.
Interpretation: Relatively Elastic Demand
The absolute value is about 2.33, which is greater than 1. In this example, quantity demanded changed by a larger percentage than price. The figures are illustrative.
Three More Types of Price Elasticity
These three graphs complete the five main elasticity categories. They show the idealized shapes economists use to explain special cases of demand responsiveness.
Perfectly Elastic
Ed = ∞
In this idealized case, buyers are willing to buy at one price, but even a small price increase above it causes demand for the product from that seller to fall to zero.
Unitary Elastic
|Ed| = 1
Quantity demanded changes by the same percentage as price. Under the standard model, total revenue remains unchanged along a unitary elastic demand curve.
Perfectly Inelastic
Ed = 0
Quantity demanded remains the same even when price changes. This is an idealized case and is uncommon in ordinary markets.
Important: These are illustrative curve shapes. The unitary elastic curve is conventionally shown as a rectangular hyperbola. Perfectly elastic and perfectly inelastic demand are theoretical limiting cases.
Five Types of Price Elasticity of Demand
Economists classify price elasticity by comparing the percentage response in quantity demanded with the percentage change in price.
Perfectly Inelastic Demand
Ed = 0Quantity demanded does not change when price changes. This is an idealized case and is uncommon in real markets.
Example: A hypothetical product that consumers must buy in exactly the same quantity regardless of price.
Relatively Inelastic Demand
Ed < 1Quantity demanded changes by a smaller percentage than price.
Example: Basic cooking salt may have relatively inelastic demand because a household usually buys a small, fairly stable quantity.
Unitary Elastic Demand
Ed = 1Quantity demanded changes by the same percentage as price.
Example: If price rises by 10% and quantity demanded falls by 10%, demand is unit elastic over that change.
Relatively Elastic Demand
Ed > 1Quantity demanded changes by a larger percentage than price.
Example: A clothing brand may face elastic demand when shoppers can easily switch to similar alternatives.
Perfectly Elastic Demand
Ed = ∞In the idealized model, buyers will purchase at one market price but none at a higher price.
Example: This is a theoretical model sometimes used to explain highly competitive markets, not a typical real-world observation.
Why Does Price Elasticity Matter?
For Households
Elasticity helps explain why a family may switch brands, postpone a non-essential purchase, or keep buying a basic product after a price increase.
For Businesses
Businesses consider how customers may respond before changing prices. A price increase can raise revenue per unit but may also reduce the number of units sold.
For Governments
Elasticity helps analysts study how consumers may respond to taxes or price changes. The actual impact also depends on supply conditions and how markets operate.
For Market Planning
Understanding customer sensitivity can help with pricing, promotions, inventory planning, and comparisons between competing products.
Real-Life Price Elasticity Examples
Clothing Business
If a clothing shop raises the price of a shirt, customers may compare other shops and online sellers. Strong competition can make demand for that particular shirt more elastic.
Everyday Groceries
A household may continue buying a similar amount of a basic grocery after a small price rise, but it may switch brands or change quantities when the increase becomes substantial.
Mobile Phones
When several phones offer similar features, a price increase may lead buyers to choose another model. Unique features or strong brand preferences can affect that response.
Factors That Influence Price Elasticity
Availability of Substitutes
When customers can easily switch to another product, demand is often more elastic. For example, shoppers may change clothing brands if one becomes more expensive.
Necessity or Luxury
Essential goods often have less elastic demand than optional purchases, although the response depends on the product and available alternatives.
Share of Income
A price increase for an expensive appliance may affect a household budget more than a small increase in the price of an inexpensive everyday item.
Time Available to Adjust
Demand may become more elastic over time because people can compare alternatives, change habits, or find replacement products.
Definition of the Market
Demand for a broad category may respond differently from demand for a specific brand. A customer might still buy shoes but switch away from one shoe brand.
Habit and Brand Loyalty
Strong habits or loyalty can reduce sensitivity to price, while customers with little brand attachment may respond more quickly to price changes.
Price Elasticity and Total Revenue
Total revenue is the price per unit multiplied by the quantity sold. When demand is relatively elastic, a price decrease tends to increase total revenue, while a price increase tends to reduce it. When demand is relatively inelastic, a price increase tends to increase total revenue, while a price decrease tends to reduce it. With unit elastic demand, total revenue remains unchanged for a movement along the same demand curve under the standard model.
These relationships describe the standard economic model. A real business should also consider costs, competitors, and whether customer demand changes for reasons other than price.
Common Misunderstandings
- Elasticity is not the same as slope. Slope measures the change in quantity against the change in price using the units on the axes; elasticity compares percentage changes.
- Inelastic does not mean unchanged. Quantity demanded can still change; its percentage change is simply smaller than the percentage change in price.
- Essential goods are not always perfectly inelastic. Buyers can adjust quantities, change brands, or find substitutes.
- Elasticity can change over time. Customers may find more alternatives when they have longer to respond.
- One example does not prove a universal rule. Elasticity depends on the market, customer group, price range, and available alternatives.
Frequently Asked Questions
What is the simplest meaning of price elasticity of demand?
It measures how much the quantity customers buy responds, in percentage terms, when the price of a product changes.
What does an elasticity of 2 mean?
An absolute elasticity value of 2 means quantity demanded changes by about 2% for each 1% price change over the relevant range, in the opposite direction for a typical downward-sloping demand curve.
Why is price elasticity usually negative?
Under the usual law of demand, a higher price is associated with a lower quantity demanded, so the percentage changes have opposite signs. Many textbooks use the absolute value when classifying elasticity.
Is price elasticity useful for small businesses?
Yes. Small businesses can compare sales before and after price changes, while keeping other influences in mind, to understand customer sensitivity and make better pricing decisions.
Note: Numerical values are illustrative examples for learning. Actual price elasticity varies by product, market, time period, and consumer circumstances.