Difference between Change in Quantity Supplied and Change in Supply

The terms Change in Quantity Supplied and Change in Supply are usually used interchangeably but are different from various prospects. Change in quantity supplied is defined as the change in the level of the quantity that the seller wishes to sell at a particular price, occurring due to a change in the price of the commodity (other factors remaining constant). Change in supply is defined as the change in the level of the quantity that the seller wishes to sell at a particular price, occurring due to changes in other factors of the supply (own price of the commodity remains the same).

What is Change in Quantity Supplied?

Change in quantity supplied occurs when the quantity supplied of a commodity changes due to a change in its price while the other factors remain constant. It is represented graphically as a movement along the same supply curve. There are two cases of movement along the same supply curve. It may be either,

1. Expansion of Supply (An Upward Movement)
2. Contraction of Supply (A Downward Movement)

When there is an expansion in the quantity supplied of a commodity because of a rise in own price of the commodity, by keeping other factors constant, it is known as an Expansion of Supply. It results in an upward movement along the same supply curve. It is also known as an Extension in Supply. When there is a contraction in the quantity supplied of a commodity because of a fall in the respective price by keeping other factors constant, it is known as a Contraction of Supply. The contraction in supply results in a downward movement along the same supply curve.

What is Change in Supply?

A supply curve is used to show the relationship between a commodity’s price and quantity supplied, assuming that all other factors remain constant. However, sooner or later, other factors will be bound to change. When one of the other factors changes, other than the own price of the commodity, then it is referred to as a Shift in the Supply Curve. Thus, changes in supply occur when the supply for a commodity changes as a result of a change in a factor other than the price of the commodity. There are two cases in the shift in supply curve,

1. Increase in Supply (A Rightward Shift)
2. Decrease in Supply (A Leftward Shift)

An increase in the supply of a commodity due to factors other than the own price of the commodity is known as an Increase in Supply. In simple terms, the supply for a commodity increases at the same price, because of changes in other factors, other than own price of the commodity. An increase in supply results in a rightward shift in the supply curve. A decrease in the supply of a commodity due to factors other than the own price of the commodity is known as a Decrease in Supply. In simple terms, the supply for a commodity decreases at the same price, because of changes in other factors, other than own prices of the commodity. A decrease in supply results in a leftward shift in the supply curve.

Difference between Change in Quantity Supplied and Change in Supply

Basis	Change in Quantity Supplied	Change in Supply
Meaning	A change in quantity supplied of a commodity due to an increase or decrease in its price while all other factors remain constant is known as a Change in Quantity Supplied.	A change in supply of a commodity as a result of a change in variable other than its price is known as a Change in Supply.
Effect on Supply Curve	It results in a movement along the same supply curve, either downwards (Contraction in Supply) or upwards (Expansion in Supply).	The shift in the supply curve is either rightwards (known as an Increase in Supply) or leftwards. (known as a Decrease in Supply).
Reason	It happens due to a change in the price of the given commodity.	It occurs as a result of other factors, such as changes in the price of substitute and complementary goods, changes in income levels, etc.