The doubling time is the period of time required for a quantity to double in size or value. It is applied to population growth, inflation, resource extraction, consumption of goods, compound interest, the volume of malignant tumours, and many other things which tend to grow over time. When the relative growth rate (not the absolute growth rate) is constant, the quantity undergoes exponential growth and has a constant doubling time or period which can be calculated directly from the growth rate.
This time can be calculated by dividing the natural logarithm of 2 by the exponent of growth, or approximated by dividing 70 by the percentage growth rate (more roughly but roundly, dividing 72; see the rule of 72 for details and a derivation of this formula).
The doubling time is a characteristic unit (a natural unit of scale) for the exponential growth equation, and its converse for exponential decay is the half-life.
For example, given Canada's net population growth of 0.9% in the year 2006, dividing 70 by 0.9 gives an approximate doubling time of 78 years. Thus if the growth rate remains constant, Canada's population would double from its 2006 figure of 33 million to 66 million by 2084.
Read more about Doubling Time: History, Examination, Where Is It Useful?, Related Concepts
Famous quotes containing the words doubling and/or time:
“My only objection to the arrangements there is the two-in-a-bed system. It is bad.... But let your words and conduct be perfectly pure—such as your mother might know without bringing a blush to your cheek.... If not already mentioned, do not tell your mother of the doubling in bed.”
—Rutherford Birchard Hayes (1822–1893)
“It would seem that man was born a slave, and that slavery is his natural condition. At the same time nothing on earth can stop man from feeling himself born for liberty. Never, whatever may happen, can he accept servitude; for he is a thinking creature.”
—Simone Weil (1909–1943)