The most natural and useful way to measure the capital stock in a particular country is to divide that stock by the annual flow of income. This gives us the capital/income ratio, which I denote by the Greek letter β. For example, if a country’s total capital stock is the equivalent of six years of national income, we write β = 6 (or β = 600%). In the developed countries today, the capital/income ratio generally varies between 5 and 6, and the capital stock consists almost entirely of private capital.
