In our last post, we established the most important rule in economics: when price goes up, quantity demanded goes down, and when price goes down, quantity demanded goes up. True for almost everything, almost everywhere. But here’s a question that rule alone can’t answer: if a hospital raises the price of a life-saving insulin shot by 20%, will people buy meaningfully less of it? And if a movie theater raises the price of popcorn by 20%, will people buy meaningfully less of that?
Common sense tells you these two situations are wildly different, even though both involve “a 20% price increase causing some decrease in quantity demanded.” Diabetics need insulin regardless of price. They’ll cut other spending before they cut their medication. Popcorn, on the other hand, is a discretionary treat with an easy substitute (your own snacks, or just skipping it) — a price hike might tank sales noticeably.
This is exactly the gap that elasticity fills. It’s the tool economists use to measure not just the direction of a response, but its magnitude, how sensitive, or insensitive, quantity is to a change in price (or income, or other factors). Once you can quantify sensitivity, a huge number of real-world puzzles suddenly make sense: why airlines charge wildly different prices for the same seat, why governments tax cigarettes instead of bread, why some businesses go bankrupt during a recession while others barely notice, and why “just raise prices” is terrible advice for some companies and excellent advice for others.
The Core Idea: Percentage Changes, Not Raw Numbers
Elasticity is formally defined as the percentage change in quantity demanded divided by the percentage change in price:
Price Elasticity of Demand = (% change in quantity demanded) / (% change in price)
Why percentages instead of raw units? Because raw numbers are misleading when you’re comparing goods with totally different scales. A $1 increase in the price of a $2 cup of coffee is a 50% price hike. A $1 increase in the price of a $50,000 car is practically nothing, 0.002%. If we measured sensitivity using dollar changes alone, we couldn’t meaningfully compare how “responsive” coffee buyers are versus car buyers. Percentages put everything on the same scale, letting us compare a candy bar to a car to a country’s currency.
Because demand curves slope downward, an increase in price (positive change) is associated with a decrease in quantity (negative change), which makes the ratio technically negative. By convention, economists usually just report the absolute value (drop the negative sign) and talk about elasticity as a positive number, with the understanding that the direction is already baked into the law of demand. So when someone says “the elasticity of demand for gasoline is 0.2,” they mean the magnitude is 0.2, and we already know quantity moves opposite to price.
Elastic, Inelastic, and the Magic Number One
Once you calculate this ratio, you sort goods into categories based on where the number lands:
Elastic demand (elasticity greater than 1). Quantity demanded changes by a larger percentage than price did. A 10% price increase might cause a 25% drop in quantity demanded. This happens with goods that have lots of substitutes, are not necessities, or take up a large share of a person’s budget. Think: a specific brand of cereal, restaurant meals, airline tickets for a leisure vacation, name-brand vs. generic medication.
Inelastic demand (elasticity less than 1). The quantity demanded changes by a smaller percentage than the price does. A 10% price increase might cause only a 2% drop in quantity demanded. This happens with necessities, goods with few substitutes, or goods that take up a tiny share of a budget. Think: insulin, salt, gasoline (in the short run), addictive substances like cigarettes.
Unit elastic demand (elasticity equal to exactly 1). Quantity demanded changes by exactly the same percentage as price. This is a useful theoretical benchmark, though it’s rare to find in the wild.
There are also two extreme theoretical cases worth knowing: perfectly inelastic demand (elasticity of zero — quantity demanded doesn’t change at all, no matter the price; a vertical demand curve) and perfectly elastic demand (elasticity approaching infinity, any price increase at all causes quantity demanded to crash to zero; a horizontal demand curve). Real-world goods rarely sit at these extremes, but they’re useful conceptual bookends. A close real-world approximation of near-perfectly-inelastic demand might be a specific drug with no substitute that a person absolutely needs to survive; a close approximation of near-perfectly-elastic demand might be a single wheat farmer trying to sell wheat above the prevailing world market price — buyers would simply go to any of thousands of other wheat farmers instead.
What Determines Elasticity?
A handful of factors reliably predict whether a good’s demand will be elastic or inelastic.
1. Availability of substitutes:
This is the single biggest driver. The more substitutes available, the more elastic demand will be, because consumers can easily switch away when price rises. Coca-Cola has relatively elastic demand because Pepsi, store-brand cola, and dozens of other drinks sit right next to it on the shelf. Table salt has very inelastic demand — there’s really no good substitute for salt in cooking, and it’s such a tiny share of any grocery bill that even a price doubling barely registers.
2. Necessity vs. luxury:
Necessities (food staples, basic utilities, essential medicine) tend toward inelastic demand because people will pay almost whatever it costs to keep getting them. Luxuries (vacations, jewellery, premium electronics) tend toward elastic demand because people can simply postpone or skip the purchase if the price isn’t right.
3. Share of the budget:
If a good eats up a large fraction of a person’s income, even a modest percentage price increase translates to real money, and people pay close attention and adjust their behavior. A 10% rise in the price of rent (a huge budget item for most renters) provokes serious behavioral responses. People downsize, get roommates, move to cheaper neighborhoods. A 10% rise in the price of dish soap (a tiny budget item) barely registers; nobody changes their cleaning habits over a few extra cents.
4. Time horizon:
This one surprises people: elasticity tends to be lower in the short run and higher in the long run, for the same good. When gas prices spike, in the short run, you mostly keep driving the same amount, you still have to get to work tomorrow, and you can’t immediately buy a new fuel-efficient car or move closer to your job. Demand is fairly inelastic. But give it a year or two, and people start buying more fuel-efficient cars, switching to public transit, or moving. Demand becomes considerably more elastic over the long run, because people have time to genuinely adjust their lives.
5. Definition breadth:
“Food” as a category has very inelastic demand. Everyone needs to eat regardless of price. But “Granny Smith apples specifically” has much more elastic demand, because if Granny Smith apples get pricey, you can switch to Gala, Fuji, or pears with barely a second thought. The narrower and more specific the category, the more substitutes exist, and the more elastic demand tends to be.
The Total Revenue Test: Why Elasticity Matters for Business
Here’s where elasticity stops being an abstract academic exercise and starts directly affecting real pricing decisions. Suppose you run a business and you’re wondering whether to raise prices. The answer hinges entirely on elasticity.
Total revenue = Price × Quantity.
If demand is inelastic, raising the price causes only a small drop in quantity. The percentage drop in quantity is smaller than the percentage rise in price, so total revenue increases. This is why airlines, hospitals, and utility companies (selling things with few good substitutes) can often raise prices and come out ahead.
If demand is elastic, raising the price causes a large drop in quantity, large enough that the loss in quantity outweighs the gain from the higher price, so total revenue decreases. This is why a small neighborhood pizza shop, competing against five other pizza places on the same street, would likely lose money overall by hiking prices: customers would simply walk to a competitor instead.
This insight flips around nicely for the opposite move, too. If you lower your price:
- With elastic demand, total revenue rises (the surge in quantity sold more than makes up for the lower price per unit). This is the logic behind sales, discounts, and “more units at a lower price” strategies for goods with lots of competition.
- With inelastic demand, total revenue falls (you’re just giving away money on a customer base that wasn’t going to change their buying habits anyway).
This is why you’ll almost never see a deep discount sale on insulin, but you’ll constantly see “30% off” sales on clothing, electronics, and restaurant meals, categories with much more elastic demand, where a lower price might genuinely draw in enough additional buyers to boost overall revenue.
Elasticity and Taxes: Who Really Pays?
Here’s one of the more counterintuitive and genuinely useful applications of elasticity: figuring out who actually bears the burden of a tax.
It’s tempting to assume that if a government taxes sellers, sellers pay the tax, and if it taxes buyers, buyers pay it. But economics shows this is mostly wrong. The actual burden of a tax (called “tax incidence”) falls more heavily on whichever side of the market is more inelastic. It is less able to adjust its behaviour in response to the tax, regardless of which side the tax is technically levied on.
Think about cigarette taxes, a classic example. Cigarette demand is highly inelastic (nicotine is addictive, and there’s no real substitute for smokers). Cigarette supply is comparatively more elastic. Tobacco companies have more flexibility around production. Because demand is more inelastic than supply, the tax burden falls mostly on consumers. Cigarette prices increase after the tax rise by nearly the full amount of the tax. Smokers still keep buying (just a bit less than before).
Now compare this to a hypothetical tax on a luxury good with lots of substitutes, like designer yachts. Demand for any one specific yacht brand is highly elastic. Wealthy buyers can switch brands, buy a slightly smaller yacht, or simply delay the purchase. If you tax yacht sellers, they can’t easily pass the cost on to buyers, because buyers will just walk away. The tax burden falls mostly on sellers instead, often eating into their profit margins rather than showing up as a price hike.
This is exactly why governments that want to both raise revenue and discourage consumption (like with cigarettes, alcohol, or sugary drinks, so-called “sin taxes”) target goods with inelastic demand. The tax revenue keeps flowing in reliably because people keep buying roughly the same amount. Even though the explicit policy goal is sometimes framed as discouraging the behavior. There’s a genuine tension here worth noting in policy debates, which we’ll touch on again later in this series.
Other Useful Elasticities
Price elasticity of demand is the most commonly discussed, but it’s not the only one worth knowing.
Income elasticity of demand:
It measures how quantity demanded responds to a change in consumer income, rather than price. Goods with positive income elasticity are called normal goods. As income rises, people buy more (most goods fall in this category). On the other hand, goods with negative income elasticity are called inferior goods. As income rises, people buy less of them, typically because they switch to better alternatives (think: generic store-brand pasta, which people often buy less of as their income grows and they can afford name brands). Goods with income elasticity greater than 1 are sometimes called luxury goods. Demand for them rises more than proportionally as income rises (designer handbags, first-class flights, fine dining).
Cross-price elasticity of demand:
It measures how the quantity demanded of one good responds to a price change in a different good. If the relationship is positive, a price increase in Good A leads to increased demand for Good B. The goods are substitutes (Coke and Pepsi). If the relationship is negative, a price increase in Good A leads to decreased demand for Good B. These goods are complements (printers and ink, hot dogs and hot dog buns).
Price elasticity of supply:
It works the same way as price elasticity of demand, but for sellers: how much does quantity supplied change in response to a price change? Goods that are easy to produce quickly and store (manufactured goods with flexible factories) tend to have elastic supply. Goods that take a long time to produce, can’t easily be stored, or depend on fixed natural resources (fresh agricultural produce right after a harvest, oil in the very short term, beachfront real estate) tend to have inelastic supply.
A Worked Example, Step by Step
Let’s make the formula concrete. Suppose a coffee shop raises the price of a latte from $4 to $5 — a 25% increase. As a result, the number of lattes sold per day drops from 100 to 80 — a 20% decrease.
Elasticity = 20% / 25% = 0.8
Since 0.8 is less than 1, demand for this coffee shop’s lattes is inelastic. What happens to total revenue? Before: $4 × 100 = $400/day. After: $5 × 80 = $400/day. The interesting part is that the revenue stayed exactly the same, which tells us this example sits almost exactly at the unit-elastic boundary in practice (the precise math of revenue and elasticity gets slightly more technical with the “midpoint method” used in many textbooks. But the intuition holds. When elasticity is below 1, revenue generally rises with a price increase. Here it’s a near-perfect wash, illustrating how close to the boundary this scenario sits.
Now suppose instead that the price increase causes lattes sold to drop from 100 to 60, a 40% decrease.
Elasticity = 40% / 25% = 1.6
Since 1.6 is greater than 1, demand is elastic, and this price increase was a bad idea from a revenue standpoint: Before: $4 × 100 = $400/day. After: $5 × 60 = $300/day. Revenue fell by $100/day even though the shop is charging more per cup. It is a clear demonstration of why “raise prices to make more money” only works when you actually know your customers’ elasticity.
Bringing It Back to Real Life
Once elasticity clicks, you start noticing it in nearly every pricing decision around you.
Why do movie theaters charge so much more for popcorn than the popcorn actually costs to make, while keeping ticket prices comparatively more competitive? Moviegoers, once inside, have highly inelastic demand for snacks (no nearby substitute once you’re seated and the previews start), while ticket buyers comparing theaters have more elastic demand and shop around more.
Why does the price of a specific generic drug barely budge even when its patent-protected, brand-name competitor still commands a hefty premium? Because once a drug becomes a true medical necessity with no real substitute, inelastic demand allows substantial pricing power.
Why do airlines use such wildly inconsistent pricing for ostensibly the same seat (book today vs. book three weeks out)? Business travelers booking last-minute tend to have far more inelastic demand (the meeting is happening whether the flight is $200 or $800), while leisure travelers booking months ahead have far more elastic demand (they can shift dates, switch airlines, or skip the trip entirely) — so airlines price-discriminate, charging each group close to what their own elasticity will bear.
What’s Next
We’ve now built two essential tools: the basic supply-and-demand framework, and the elasticity lens that tells us how sensitive that framework really is in any given market. But so far, we’ve mostly imagined markets with lots of buyers and sellers, none of whom has much individual power over price — what economists call perfect competition. Real markets often look nothing like that. Some markets have a single dominant seller (a monopoly) and some have just a handful of giant competitors (an oligopoly). Some have many sellers, but each offering a slightly different product (monopolistic competition). In our next post, we’ll explore these different market structures, and you’ll see how the number and behavior of competitors in a market dramatically changes pricing power, profits, and the overall efficiency of the outcome for society.