Microeconomics
Marginal Utility
Diminishing returns of additional units — basis of consumer choice theory
Marginal utility is the additional satisfaction (utility) gained from consuming one more unit of a good. Law of diminishing marginal utility: each additional unit gives less satisfaction than the previous. First slice of pizza: very satisfying. Tenth slice: probably nauseating. Foundation of: consumer choice theory, demand curves, optimal allocation. Discovered by Jevons, Menger, Walras (1870s) — "marginal revolution" in economics. Total utility maximized by spending until last dollar gives equal marginal utility per dollar across goods. Critiques: utility hard to measure; cardinal vs ordinal utility.
- DefinitionAdditional utility from one more unit
- LawDiminishing marginal utility (typically)
- DiscoveredJevons, Menger, Walras (1870s)
- ApplicationConsumer choice; demand curves
- OptimizationSpend until MU/P equal across goods
- TypeCardinal (measurable) or ordinal (rankings)
Interactive visualization
Press play, or step through manually. The visualization is yours to drive — try it before reading on.
Watch the 60-second explainer
A condensed visual walkthrough — narrated, captioned, under a minute.
Why marginal utility matters
- Consumer theory. Foundation of demand.
- Pricing. Setting prices.
- Decision-making. Optimal allocation.
- Public policy. Welfare analysis.
- Behavioral economics. Understanding choices.
- Marketing. Anticipating consumer response.
- Education. Foundational microeconomics.
Common misconceptions
- Total utility same as marginal. Different — total accumulates.
- Always diminishing. Most cases; exceptions exist.
- Easy to measure. Often hard; cardinal utility difficult.
- Same for everyone. Personal preferences vary.
- Just for goods. Applies to time, money, anything valued.
- Settled theory. Behavioral economics challenges some assumptions.
Frequently asked questions
What's marginal utility?
Additional satisfaction from consuming one more unit. Total utility from 0 units: 0. After 1 pizza slice: 10 utility (MU = 10). After 2 slices: 18 total (MU = 8 — diminishing). After 3: 24 (MU = 6). Each additional unit gives less. Why? Decreasing intensity of need; satiation. Foundation of demand curves: more units worth less per unit.
What's diminishing marginal utility?
As consumption increases, additional utility decreases. Common pattern. Reasons: (1) Most pressing needs satisfied first. (2) Physical capacity limits. (3) Hedonic adaptation. Examples: water (first sip thirsty: huge utility; tenth: small). Money (rich person values $100 less than poor person). Food, leisure, etc. Universal economic phenomenon.
How does this drive demand?
Higher quantities have lower marginal utility. So: willing to pay less per unit. First unit: high willingness to pay. Hundredth: low. Demand curve slopes downward. Each individual's demand reflects marginal utility schedule. Aggregate demand: sum of individual demands.
How is utility maximized?
Spend each dollar where it gives most marginal utility. At optimum: marginal utility per dollar equal across all goods. MUx/Px = MUy/Py = ... If MUx/Px > MUy/Py: switch spending from y to x. Increases x's MU/P (less of it), decreases y's MU/P. Continue until equal. Utility maximized.
What's cardinal vs ordinal utility?
Cardinal: utility measured numerically. "Drinking water gives me 10 utils." Total utility quantifiable. Ordinal: just rankings. "I prefer apple to orange." No numerical value. Modern preference: ordinal — fewer assumptions. Indifference curves use ordinal utility. Cardinal: more powerful but harder to defend.
What's the marginal revolution?
1870s economic revolution. William Stanley Jevons (UK), Carl Menger (Austria), Léon Walras (France) — independently developed marginal analysis. Replaced labor theory of value (classical economics) with marginal utility theory. Foundation of neoclassical economics. Mathematical: optimization at margins. Influenced: consumer theory, producer theory, modern microeconomics.
Are there exceptions to diminishing utility?
Some. (1) Collectibles: more might increase value (10 stamps in collection more than sum of separate). (2) Necessities: water has high utility until satiated. (3) Addiction: opposite — increasing marginal utility (more wanted). (4) Status goods: more might be more valued (for status). Generally diminishing applies broadly but specific cases differ.