Consumer Surplus

Consumer surplus is a measure of the welfare that people gain from the consumption of goods and services with regard to the prices they pay for it.

Consumer surplus is the difference between the total amount that consumers are willing to pay and what they actually pay for a good or service (indicated by the demand curve) . Consumer surplus is a measure of welfare. 

The amount of consumer surplus can be derived from the demand curve. The price of a commodity is determined by the interaction of demand and supply curve. 

Consumers always like to feel like they are getting a good deal on the goods and services they buy and consumer surplus is simply an economic measure of this satisfaction. For example, assume a consumer goes out shopping for a CD player and he or she is willing to spend $250. When this individual finds that the player is on sale for $150, economists would say that this person has a consumer surplus of $100.