In economics, the term "quantity supplied" refers to which of the following?
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Economics · Foundations
Supply
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In 30 seconds
Supply The whole relationship between a good's price and the quantity producers are willing and able to sell, shown as a schedule or a curve. Full entry → is the whole relationship between a good's price and the quantity producers are willing and able to sell. The Law of supply The regularity that, other things equal, a higher price raises the quantity supplied and a lower price lowers it. Full entry → says that, holding everything else constant, a higher price brings a larger Quantity supplied The specific amount producers offer at one particular price; a single point on the supply curve. Full entry →, because extra output becomes more profitable. That gives an upward-sloping Supply curve A graph of the supply schedule, with price on the vertical axis and quantity on the horizontal axis, sloping upward. Full entry →. Watch two distinctions: quantity supplied is one point at one price, while supply is the entire curve; and the good's own price moves you along the curve, whereas other factors shift the whole curve.
Why this matters
Supply is half of the supply-and-demand model that explains almost every price you see, from gasoline to apartments to concert tickets. Getting it precise keeps you from a mistake that trips up beginners and pundits alike: confusing a price-driven movement along the curve with a genuine change in supply caused by costs, technology, or policy. That distinction is exactly what you need to reason about a tax on producers, a bumper harvest, a chip shortage, or new firms entering a market. Master supply on its own and the equilibrium, elasticity, and cost topics that build on it become far easier, because you already know what does and does not move a supply curve.
The college version
Supply is a relationship, not a single amount
In everyday speech, "supply" sounds like a fixed pile of goods sitting in a warehouse. In economics it means something more precise: supply is the entire relationship between the price of a good and the quantity producers are willing and able to sell, measured over some period and holding other influences constant. Because a producer's willingness to sell changes as the price changes, supply is best pictured as a list of price-quantity pairs, not one number. Presented as a table, that list is a Supply schedule A table pairing each possible price with the quantity supplied at that price. Full entry →; drawn on a graph with price on the vertical axis and quantity on the horizontal axis, it is a supply curve. Two words matter here. Supply refers to the whole schedule or curve. Quantity supplied refers to just one point on it, the specific amount offered at one specific price. Saying "supply rose" when you mean "a higher price drew out a larger quantity supplied" is the single most common error in this topic, and the rest of the lesson is built around avoiding it.
The law of supply and why the curve slopes up
The law of supply states that, all other things equal (Ceteris paribus Latin for 'all other things equal'; the assumption that only the named variable changes while everything else is held constant. Full entry →), a rise in a good's price increases the quantity supplied and a fall in price decreases it. Price and quantity supplied move in the same direction, so the supply curve slopes upward from left to right. The reason is profit. Producing extra units costs something, and those costs typically rise as a firm pushes output higher. A higher selling price makes it worthwhile to cover those rising costs and produce more, and it also draws in higher-cost producers who would sit out at lower prices. A lower price does the reverse. The phrase "all other things equal" is doing real work: the law describes what happens when only the good's own price changes and everything else, such as input costs and technology, stays put. OpenStax's illustrative gasoline schedule shows the pattern cleanly, with quantity supplied climbing from 500 million gallons at $1.00 per gallon to 720 million gallons at $2.20 per gallon.
Movement along the curve versus a shift of the curve
This is the distinction that separates a confident reader from a confused one. When the good's own price changes and nothing else does, you slide from one point on the fixed supply curve to another. Economists call this a movement along the curve, or a change in quantity supplied. The curve itself has not moved; you have simply read off a different point. When some factor other than the good's own price changes, the amount producers will offer at every price changes, so the whole curve relocates. That is a shift, or a change in supply. A rightward shift means more is supplied at each price and is called an Increase in supply A rightward shift of the supply curve, meaning more is supplied at every price. Full entry →; a leftward shift means less at each price and is a decrease in supply. The test is simple: ask what changed. If it was the good's own price, you have a movement. If it was anything else, you have a shift.
What shifts the supply curve
Several determinants can shift supply, and most work by changing the cost or profitability of producing at any given price. Input (factor) prices: cheaper labor, materials, or energy lower costs and shift supply right; more expensive inputs shift it left. Technology: a cost-reducing innovation lets the same inputs produce more output, shifting supply right. Taxes and subsidies: a per-unit tax or costly regulation raises production costs and shifts supply left, while a subsidy lowers costs and shifts it right. Number of sellers: more firms in the market add to the quantity offered at every price and shift supply right; firms exiting shift it left. Expectations: if producers expect a higher price later, they may hold back output now, reducing current supply. Prices of related goods in production: when a firm can make either of two goods with the same resources, a rise in one good's price pulls resources toward it and shifts the supply of the other good left. In every case the trigger is something other than the good's own price, which is precisely why it shifts the curve instead of moving along it. Where supply meets demand determines the market price and quantity, but equilibrium is its own topic; here the goal is simply to know what supply is and what moves it.
Eli explains
The same idea, in plain words
Explain it like I’m 10
Supply is a producer's whole answer to the question 'how much would you sell at each price?' The answer is a list, not one number: at a low price they'll sell a little, at a high price they'll sell a lot, because a higher price makes it worth the extra cost of making more. If only the price changes, you just pick a different amount off the same list. But if something else changes, like their materials getting cheaper or a new machine helping them work faster, they rewrite the whole list and will sell more at every price. Changing the price walks you along the list; changing anything else replaces the list.
Picture it like this
Think of a lemonade stand with a sign: '$1 a cup, I'll make 10; $2 a cup, I'll make 25.' That sign is the supply curve. If a customer offers more per cup, you slide down your own sign and make more. But if your family suddenly gives you free lemons, you tear up the sign and write a new one promising more cups at every price. Price changes move you along the sign; free lemons give you a whole new sign.
Where the picture stops working
The lemonade sign makes supply look like one child's tidy decision, but a real supply curve is the combined offering of many producers, and their costs rise as total output grows rather than staying flat. The analogy also treats the new sign as instant, whereas shifting supply in the real world can take time as firms retool, hire, or enter the market.
Worked example
Use OpenStax's gasoline supply schedule. At $1.00 per gallon producers offer 500 million gallons; at $1.20, 550; at $1.40, 600; at $1.60, 640; at $1.80, 680; at $2.00, 700; and at $2.20, 720. Now test the two moves. First, the price rises from $1.60 to $2.00 with nothing else changing: quantity supplied climbs from 640 to 700 million gallons. That is a movement along the curve, because only the good's own price changed. Second, suppose a new refining technology cuts costs so producers will offer 60 million more gallons at every price. Now $1.60 fetches 700 instead of 640, and $2.00 fetches 760 instead of 700. The whole schedule has shifted right, an increase in supply, because the trigger was technology, not price.
Key takeaway
Supply is the whole upward-sloping relationship between price and quantity supplied. The good's own price moves you along the curve; anything else, cost, technology, taxes, sellers, expectations, or related-good prices, shifts the entire curve.
Quick check
3 questions here, of 5 in this lesson’s practice set. Answers stay hidden until you check.
Holding all else constant, why does the supply curve slope upward?
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The market price of wheat rises while every other factor stays the same. On the wheat supply diagram, this is best described as:
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Study tools & related lessonsYou’ll learn to · Common mistakes · Easily confused · Key vocabulary · Related
You’ll learn to
- Define supply and quantity supplied and distinguish the whole curve from a single point on it
- State the law of supply and explain why the supply curve slopes upward
- Read a supply schedule and connect it to the supply curve
- Distinguish a movement along the supply curve from a shift of the curve
- Identify the determinants that shift supply and predict the direction of the shift
Common mistakes
Saying 'supply increased' when the good's price rose and more was sold.
A price change moves you along a fixed curve, raising the quantity supplied. Supply (the curve) only 'increases' when a non-price determinant shifts it right.
Treating quantity supplied and supply as the same thing.
Quantity supplied is one point at one price; supply is the entire schedule or curve. Keep the words distinct.
Thinking the supply curve slopes upward because sellers are greedy.
It slopes up because producing more costs more, so a higher price is needed to make additional units worth supplying. It is about rising costs, not attitude.
Assuming a change in demand or the good's own price shifts the supply curve.
Only supply determinants (input prices, technology, taxes/subsidies, number of sellers, expectations, related production goods) shift the supply curve; the good's own price moves along it.
Reading a rightward shift as 'higher price' instead of 'more at every price.'
A rightward shift is an increase in supply: a larger quantity offered at each price. On its own it tends to lower the equilibrium price, not raise it.
Easily confused
Quantity supplied vs. Supply
Quantity supplied is one amount at one price (a point); supply is the full price-quantity relationship (the whole curve).
Movement along the curve vs. Shift of the curve
The good's own price changing moves you along a fixed curve; a determinant changing relocates the entire curve.
Increase in supply (rightward shift) vs. Decrease in supply (leftward shift)
Rightward means more offered at every price (e.g., lower input costs or new sellers); leftward means less at every price (e.g., a new tax or firms exiting).
Key vocabulary
- Supply
- The whole relationship between a good's price and the quantity producers are willing and able to sell, shown as a schedule or a curve.
- Quantity supplied
- The specific amount producers offer at one particular price; a single point on the supply curve.
- Law of supply
- The regularity that, other things equal, a higher price raises the quantity supplied and a lower price lowers it.
- Supply schedule
- A table pairing each possible price with the quantity supplied at that price.
- Supply curve
- A graph of the supply schedule, with price on the vertical axis and quantity on the horizontal axis, sloping upward.
- Ceteris paribus
- Latin for 'all other things equal'; the assumption that only the named variable changes while everything else is held constant.
- Movement along the supply curve
- A change in quantity supplied caused by a change in the good's own price, sliding between points on a fixed curve.
- Shift of the supply curve
- A change in supply that moves the entire curve because a non-price determinant changed the amount offered at every price.
- Determinants of supply
- Factors other than the good's own price that shift supply: input prices, technology, taxes and subsidies, number of sellers, expectations, and prices of related goods in production.
- Increase in supply
- A rightward shift of the supply curve, meaning more is supplied at every price.
Sources & references
- Principles of Economics 2e, Section 3.1: Demand, Supply, and Equilibrium in Markets for Goods and Services — OpenStax (Rice University)
- Principles of Economics 2e, Section 3.2: Shifts in Demand and Supply for Goods and Services — OpenStax (Rice University)
- Principles of Microeconomics (CDN Edition), Section 3.4: Changes in Supply — eCampusOntario Pressbooks (adapted from University of Minnesota Principles of Economics)
EliExplains lessons are original prose written from the open, credible references above. See Copyright & Licensing.
Researched 2026-08-19
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