What Is Elasticity in Economics? Meaning, Formula and Examples
By Markets & Investing DeskUpdated Nov 10, 2026
Definition
Elasticity measures how strongly one economic variable responds to a change in another, expressed as a ratio of percentage changes, most often how quantity demanded reacts to price.
Key takeaways
- Price elasticity of demand equals the percentage change in quantity demanded divided by the percentage change in price.
- When demand is elastic, with an absolute value above 1, a price increase lowers total revenue.
- Income elasticity above 1 marks a luxury, while a negative value marks an inferior good.
- Positive cross-price elasticity signals substitutes, and a negative value signals complements like printers and ink.
Elasticity in economics is a measure of how strongly one variable responds to a change in another, expressed as a ratio of percentage changes. Most often it describes how much the quantity demanded of a good changes when its price changes, which is called price elasticity of demand. When demand is elastic, buyers respond sharply to a price change. When it is inelastic, they keep buying close to the same amount.
How Elasticity Works
Elasticity uses percentages instead of raw units so that responses can be compared across goods. A drop of 1,000 gallons of fuel and a drop of 1,000 airline seats cannot be compared side by side, but a 5% drop in each can, whatever the units or price levels.
The formula
The general form is:
Elasticity = % change in quantity ÷ % change in the influencing variable
For price elasticity of demand:
PED = % change in quantity demanded ÷ % change in price
Because a higher price usually lowers quantity demanded, PED is normally negative: the two variables move in opposite directions. Economists often drop the minus sign and talk about the absolute value, so “an elasticity of 1.5” usually means −1.5. For cross-price and income elasticity, the sign carries information and should be kept.
Worked example (hypothetical)
Suppose a café raises the price of a sandwich from $10 to $12, and daily sales fall from 100 to 70.
- Simple percentage method: price rises 20% (2 ÷ 10), quantity falls 30% (30 ÷ 100). PED = −30% ÷ 20% = −1.5.
- Midpoint (arc) method: divide each change by the average of the two values. Price change = 2 ÷ 11 ≈ 18.2%. Quantity change = −30 ÷ 85 ≈ −35.3%. PED ≈ −1.94.
The simple method depends on which point you start from. Running the change backward (from $12 to $10) gives a different simple result, while the midpoint method gives the same figure in both directions. Either way, demand here is elastic. Revenue confirms it: 100 × $10 = $1,000 before, 70 × $12 = $840 after.
Interpreting the result
| Absolute value | Term | What a price increase does to total revenue |
|---|---|---|
| Greater than 1 | Elastic | Revenue falls |
| Equal to 1 | Unit elastic | Revenue unchanged |
| Less than 1 | Inelastic | Revenue rises |
| Infinite | Perfectly elastic | Any increase drops quantity to zero |
| Zero | Perfectly inelastic | Quantity does not change at all |
Perfect elasticity and perfect inelasticity are theoretical limits. A perfectly elastic demand curve is horizontal, a textbook approximation for a single seller in a highly competitive market, such as one farmer selling a standardized crop, who loses all buyers above the market price. A perfectly inelastic curve is vertical, a rough model for a life-saving drug with no alternative.
Types of Elasticity
Price elasticity of demand measures buyers’ response to the good’s own price, as in the example above.
Income elasticity of demand divides the percentage change in quantity demanded by the percentage change in income. A positive value marks a normal good. A value above 1 marks a luxury, where spending grows faster than income. A negative value marks an inferior good, which people buy less of as they earn more.
Cross-price elasticity of demand compares the change in demand for one good with a price change in another. A positive value means the goods are substitutes: if one airline raises fares, demand for rival airlines rises. A negative value means they are complements, such as printers and ink cartridges.
Price elasticity of supply measures how much producers change the quantity they offer when price changes. It is usually positive, because higher prices encourage more production. It depends on how quickly firms can add labor, equipment and materials, the factors of production behind output.
What Makes Demand Elastic or Inelastic
- Close substitutes. Goods with many alternatives, such as one airline’s fares or one brand of cereal, tend to be elastic.
- Necessity versus luxury. Staples such as bread, housing, healthcare and gasoline tend to be inelastic.
- Share of the budget. A price change on a small purchase like salt barely registers. The same percentage change on a car or rent draws a larger response.
- Time. Demand is usually more elastic in the long run. A driver facing higher gasoline prices may keep commuting the same way this month but buy a more efficient car or move closer to work over several years.
- Market definition. Demand for “food” is inelastic. Demand for one restaurant’s burger is far more elastic.
Why Elasticity Matters
Businesses use price elasticity to set prices. A firm facing inelastic demand can raise prices and increase revenue. A firm facing elastic demand risks losing customers, which is why companies in fiercely competitive industries often act as price takers and accept the prevailing market price.
Governments use elasticity to predict the effects of taxes. Excise taxes on inelastic goods such as tobacco and fuel raise revenue reliably because consumption falls only modestly. The share of a tax borne by buyers versus sellers also depends on the relative elasticities of demand and supply: the less elastic side bears more of it.
Consumers and investors benefit too. Companies selling inelastic products tend to have steadier sales through price swings, while supply elasticity signals whether a price spike will draw out new production or lead to lasting scarcity.
Limitations
Elasticity estimates rely on the assumption that other factors stay constant (ceteris paribus). In real data, income, tastes and competitors’ prices change at the same time, so isolating the effect of price is difficult. Because elasticity varies along a demand curve, a single figure applies only to a specific price range, and estimates based on past behavior may not hold after a market shift.
Elasticity vs. Slope
Elasticity and the slope of a demand curve are often confused. Slope measures the change in units (dollars per item) and depends on the units chosen. Elasticity measures percentage changes and has no units. A straight-line demand curve has a constant slope, but its elasticity changes at every point along it: demand is elastic at high prices and inelastic at low prices. A steep curve suggests inelastic demand only when two curves are drawn on the same scale.
The Bottom Line
Elasticity matters to businesses setting prices, governments planning taxes, and investors judging how steady a company's sales will be. Firms with inelastic demand can raise prices and increase revenue, while those facing elastic demand risk losing customers. Any single estimate applies only to a specific price range and assumes other factors stay constant, so past figures may not hold after a market shift.
