--- title: "Perfectly Elastic Demand | Principles of Macroeconomics" description: "Perfectly elastic demand is when quantity demanded drops to zero after any price increase, shown by a horizontal demand curve in Principles of Macroeconomics." canonical: "https://fiveable.me/principles-macroeconomics/key-terms/perfectly-elastic-demand" type: "key-term" subject: "Principles of Macroeconomics" unit: "Unit 5" --- # Perfectly Elastic Demand | Principles of Macroeconomics ## Definition Perfectly elastic demand is demand that responds infinitely to even the smallest price change. In Principles of Macroeconomics, it shows up as a horizontal demand curve. ## What It Is Perfectly elastic demand is the case where buyers will purchase a good at one exact market price, but they will not buy any of it if the price rises by even a tiny amount. In Principles of Macroeconomics, this is drawn as a horizontal demand curve at the going market price, because quantity demanded can change from a lot to none with no change in price. This is an extreme model, not something you usually see in everyday markets. Macroeconomics uses it to show what happens when buyers see products as completely interchangeable and have no reason to accept a higher price from one seller. If one seller charges even slightly more, consumers switch away immediately. The easiest way to picture it is a perfectly competitive market with a tiny change in price. At the set market price, a single firm can sell as much as it can produce. But if it charges more, buyers go elsewhere, so its quantity demanded falls to zero. That is why the demand curve is flat from the firm’s point of view. This is different from just being "very responsive" to price. Perfectly elastic demand is the limiting case of elasticity, meaning the response is so strong that the curve becomes flat. Real markets rarely behave this way exactly, but the model helps you see how strong competition and close substitutes push firms toward price-taking behavior. A common mix-up is thinking "perfectly elastic" means consumers always buy unlimited amounts. It does not. It means quantity demanded is unlimited only at one specific price. The moment price changes, the market reaction is immediate and total. In macro, this idea connects to pricing decisions and revenue. If a seller in a highly competitive market raises price, it can lose all sales. That makes perfectly elastic demand a useful benchmark for understanding why some firms have almost no pricing power. ## Why It Matters Perfectly elastic demand matters because it gives you a clean model for price-taking behavior, which shows up all over Principles of Macroeconomics when you compare competitive markets to markets with more control over price. If demand is perfectly elastic, a firm cannot raise price without losing all buyers, so it has to accept the market price. That idea helps you reason through total revenue, pricing strategy, and market structure. In a problem set or graph question, you may be asked what happens if price changes. With perfectly elastic demand, the answer is simple: quantity demanded falls from all of it to none of it, which is why the firm’s demand curve is horizontal. It also gives you a useful reference point for elasticity of demand. Most goods fall somewhere between perfectly elastic and perfectly inelastic, so this term helps you place real-world products on that spectrum. The more substitutes consumers have, the closer demand gets to this extreme. You’ll also see the logic behind why a seller of a nearly identical product, like a commodity, has very little room to charge above market price. Even a small markup can send buyers to competitors. That’s the same reasoning macro uses when it talks about competition, market efficiency, and how firms react to prices rather than set them freely. ## Connections ### Elasticity of Demand Perfectly elastic demand is the extreme case of elasticity of demand. Instead of just measuring whether buyers are sensitive to price, it shows the strongest possible response, where any price increase wipes out quantity demanded. If you understand regular elasticity first, this term makes the whole scale easier to read. ### Demand Curve The demand curve for perfectly elastic demand is horizontal, which is the visual clue to look for on a graph. That shape tells you price stays fixed while quantity can vary at that one price. If the line slopes downward, the demand is not perfectly elastic. ### Price Sensitivity Price sensitivity is the everyday idea behind this term. Perfectly elastic demand is what price sensitivity looks like when it reaches the maximum possible level. In practice, the more sensitive buyers are, the more a firm has to worry about losing customers after a price increase. ### [Perfectly Inelastic Demand](/principles-macroeconomics/key-terms/perfectly-inelastic-demand) This is the opposite extreme. Perfectly inelastic demand means quantity demanded does not change at all when price changes, while perfectly elastic demand means quantity demanded disappears if price rises even a little. Comparing the two helps you see the full range of demand responsiveness. ## On the AP Exam A quiz item or graph question will usually ask you to identify the shape of demand, explain what happens after a price change, or compare it with another elasticity case. If you see a horizontal demand curve, you should recognize perfectly elastic demand and say that the seller can charge only one market price. If price rises above that level, quantity demanded drops to zero. For a written response, use the term to explain why a firm in a highly competitive market has little pricing power. If the prompt gives you a scenario with close substitutes, connect that to high price sensitivity and explain why buyers switch quickly. On graph-based problems, describe the curve first, then interpret the market result. ## Perfectly Elastic Demand vs Perfectly Inelastic Demand These two are easy to mix up because they are both extreme cases, but they behave in opposite ways. Perfectly elastic demand means quantity demanded changes infinitely when price changes, while perfectly inelastic demand means quantity demanded does not change at all. On a graph, perfectly elastic demand is horizontal and perfectly inelastic demand is vertical. ## Key Takeaways - Perfectly elastic demand means buyers will purchase any quantity at one exact price, but none if the price changes even slightly. - On a graph, perfectly elastic demand is shown as a horizontal demand curve. - This term is an extreme model, so it is mainly used to think about idealized competitive markets and price-taking firms. - The more close substitutes a good has, the more its demand can behave like this case. - If a firm with perfectly elastic demand raises price, it loses all buyers. ## FAQs ### What is perfectly elastic demand in Principles of Macroeconomics? Perfectly elastic demand is demand that responds infinitely to a price change. In Principles of Macroeconomics, it means buyers will buy at one market price but will not buy at any higher price. The demand curve is horizontal. ### What does a perfectly elastic demand curve look like? It looks like a flat horizontal line at the market price. That shape shows that quantity demanded can vary, but only at that one price. If price moves up even a little, quantity demanded falls to zero. ### Is perfectly elastic demand realistic? Not usually. It is a simplified model economists use to represent extreme price sensitivity, especially in very competitive markets. Real goods are more often highly elastic than perfectly elastic. ### How is perfectly elastic demand different from perfectly inelastic demand? They are opposites. Perfectly elastic demand means quantity demanded changes drastically when price changes, while perfectly inelastic demand means quantity demanded does not change at all. Their graphs are horizontal versus vertical. ## Related Study Guides - [5.3 Elasticity and Pricing](/principles-macroeconomics/unit-5/3-elasticity-pricing/study-guide/EGzdnMCS0vp8C915) ## About This Document Canonical Fiveable pages are available as Markdown at the same path plus `.md`. - [llms.txt](https://fiveable.me/llms.txt): index of Fiveable's sections and URL patterns - [llms-full.txt](https://fiveable.me/llms-full.txt): complete subject and unit listing - [MCP server](https://fiveable.me/mcp): call Fiveable as tools instead of fetching pages (`https://fiveable.me/api/mcp`) - [MCP server for AP teachers](https://fiveable.me/mcp/teachers): a teacher's classes, assignments and AP-rubric grading (`https://fiveable.me/api/mcp/teacher`) ## Structured Data ```json {"@context":"https://schema.org","@graph":[{"@type":"LearningResource","@id":"https://fiveable.me/principles-macroeconomics/key-terms/perfectly-elastic-demand#resource","name":"Perfectly Elastic Demand | Principles of Macroeconomics","url":"https://fiveable.me/principles-macroeconomics/key-terms/perfectly-elastic-demand","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/principles-macroeconomics/key-terms/perfectly-elastic-demand#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:24:03.605Z","isPartOf":{"@type":"Collection","name":"Principles of Macroeconomics Key Terms","url":"https://fiveable.me/principles-macroeconomics/key-terms"},"author":{"@type":"Organization","@id":"https://fiveable.me/editorial#content-team","name":"Fiveable Content Team","url":"https://fiveable.me/editorial","parentOrganization":{"@id":"https://fiveable.me/#organization"},"member":[{"@type":"Person","name":"Amanda DoAmaral","sameAs":["https://www.linkedin.com/in/adoamaral"]},{"@type":"Person","name":"Becky Bahr","sameAs":["https://www.linkedin.com/in/becky-bahr-b52743132"]}]},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/principles-macroeconomics/key-terms/perfectly-elastic-demand#term","name":"Perfectly Elastic Demand","description":"Perfectly elastic demand is demand that responds infinitely to even the smallest price change. 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