Doubling Time Formula

Growth proponents may claim that "small" (such as 1% per year) increases in growth will not lead to noticeable changes in a community. The doubling time formula is a great tool for rebutting this argument. The formula calculates the number of years that it will take a population to double in size, given a certain growth rate per year. The exact formula is

n   =   ln 2
ln[1 + (r/100)]

where n is the doubling time (in years) and r is the growth rate (in percent per year).

For instance, when r is 1 (one percent growth per year), n equals 69.7 (the approximate life span of an American). So if your community's population were to grow by 1% per year, the number of people around you would double during your lifetime.

The formula can be approximated by the equation: n = 70/r

A fascinating lecture by Dr. Al Bartlett on the doubling formula and the incredible ramifications of continued growth is available on the Global Public Media website.

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