For most purposes, the overall growth rate is the more frequently utilized. This length of time is determined by dividing the growth rate into 70. The number 70 comes from the natural log of 2, which is .70. Thus, in 2070, if the current rate of growth remains constant, Canada's population will double from its current 31 million to 62 million. We can expect the world's population of 6 billion to become 12 billion by 2054 if current growth continues.
Most European countries have low growth rates.
Germany's natural growth rate of -0.1 can not be used to determine doubling time because the population is actually shrinking in size. Many Asian and African countries have high growth rates. If population growth continued at the same rate for the following century, by 2200 Afghanistan's population would be 26.6 billion, which is more than four times the current world population - a ridiculous expectation. As you can see, population growth percentages is better utilized for short term projections. Increased population growth generally represents problems for a country - it means increased need for food , infrastructure, and services.