Glossary term
Equilibrium Quantity
Equilibrium quantity is the amount bought and sold when supply and demand are balanced at the equilibrium price.
Updated
Read time
What Is Equilibrium Quantity?
Equilibrium quantity is the amount of a good or service bought and sold when supply and demand are balanced. It occurs at the equilibrium price, where the quantity buyers want to purchase equals the quantity sellers want to supply.
In a supply-and-demand graph, equilibrium quantity is found at the point where the demand curve and supply curve intersect. The corresponding price is the equilibrium price.
Key Takeaways
- Equilibrium quantity is the quantity traded when supply equals demand.
- It occurs at the equilibrium price.
- A shortage exists when quantity demanded exceeds quantity supplied at a price.
- A surplus exists when quantity supplied exceeds quantity demanded at a price.
- Changes in supply or demand can move the equilibrium quantity.
How Equilibrium Quantity Works
If price is too low, buyers want more than sellers provide, creating a shortage. If price is too high, sellers provide more than buyers want, creating a surplus. Market pressure can push price and quantity toward equilibrium.
Equilibrium quantity changes when the demand curve or supply curve shifts. For example, higher consumer income may increase demand for a normal good, raising equilibrium quantity. Higher input costs may reduce supply, lowering equilibrium quantity.
The direction of the quantity change depends on which curve shifts and how much. A demand increase usually raises equilibrium quantity, while a supply decrease often lowers it and raises price.
Supply and Demand Outcomes
Market condition | Quantity relationship | Typical pressure |
|---|---|---|
Equilibrium | Quantity demanded equals quantity supplied | Market clears |
Shortage | Quantity demanded exceeds quantity supplied | Price tends to rise |
Surplus | Quantity supplied exceeds quantity demanded | Price tends to fall |
Demand increase | Buyers want more at each price | Equilibrium quantity may rise |
Limits and Misunderstandings
Equilibrium quantity is a model concept, not a guarantee that markets are calm or fair. Real markets can face sticky prices, regulation, contracts, rationing, inventory constraints, and sudden shocks.
It is also not the same as maximum possible output. It is the quantity traded at the price where buyer and seller plans align under the model's assumptions.
The concept is still useful even when real markets are messy. Equilibrium quantity gives analysts a reference point for asking whether a price control, shortage, surplus, subsidy, or shock is pushing trade away from the market-clearing level.
The Bottom Line
Equilibrium quantity is the market-clearing amount bought and sold when supply and demand are balanced. It helps explain how prices and quantities adjust when market conditions change.