When the size of an economy is measured, only the amount of final consumption is measured, all other exchanges in the economy that lead to consumption are not considered, because their value is contained within the final product. Because their value is contained within the final product, to count them separately would be to count them twice.

The size of an economic system is measured by the value of all of the products that are consumed in it, usually over a period of a year. This value is the gross product of that economic system. If the economic system being considered is a nation, as it usually is, then this is the gross national product  (GNP) or the gross domestic product (GDP.)

This page is linked from:

why the economy is all about consumption 

Agree? Disagree? Make a comment!  (Comments are moderated)