In economics, the distinction is often made between stock magnitudes and flow magnitudes. A "stock" is something one has accumulated in the past and has on hand at any one time. It would be measured using simple units (such as dollars or tons). On the other hand, a "flow" is something that occurs over time and would be measured as dollars per year or tons per month or similar. The diagram contrasts the flows of new investment (and of depreciation or depletion) with the stock of capital currently on hand.

A person or country might have stocks of money, financial assets, liabilities, real means of production, capital, and human capital (or labor-power). Other flow magnitudes besides those shown in the diagram include income, spending , saving, debt repayment, and labor.

see saving.