# Population Calculators

One important component of biology today is predicting populations. Population growth calculations can be used to predict how long it will be until you need to buy a new petri dish for your expanding colony of bacteria, or to see how long it will be before an endangered species becomes commonplace once more. Don't really care about biology, though? Well, you're in luck. Population growth calculations are also used by governments across Canada AND the world to help plan new developments for our growing population, such as schools, food production levels, and hospitals. It has even been estimated by The United Nations Populations Fund that in 2083, the world will have 10 billion people living on it! As you can probably now tell, studies and calculations involving populations are pretty important. Keep reading to learn more, and calculate some population growth yourself!

## Population Growth

One of the most common calulations used in determining population growth, is the final population being equal to the starting population, multiplied by e to the power of rate of growth multiplied by time (look at the visual below). The letter 'e' represents the famous and extreamly useful mathematical constant and irrational number, which is sometimes called Euler's number, and when multiplied to the power of another variable, is called the exponential function. Its first few digits are: 2.7182818284590452353602874713527, as it is the sum of 1 + 1/1 + 1/1*2 + 1/1*2*3 + ..., and so on. It is used in this equation, because population growth is exponential, which means that their rate of growth itself grows at an increasingly rapid rate compared to the total size of the population. To calculate a population's growth yourself, fill in the variables of this equation in the form below, and press "Show the Growth". Below the button, your population's growth will be shown in steps by year.

p_o (initial population):
r (growth rate in percent):
t_1 (starting time):
t_2 (ending time):

## Doubling Time

Doubling time is the length of time that a given population will take to double its size. To calculate the doubling time, we use the Rule of 70, where you divide 70 (the 'magic' number in this case) by the growth rate of the specific population. However, because the growth rate of a population can change over time, doubling time is not always accurate; it's mostly used in estimations. To calculate the doubling time of a population, just input the size and growth rate (in a percentage) of your population below, click "Double the Population", and the answer will output below. Click on the equation and example below to learn more about doubling time.

Initial Population:
Growth Rate (in percent):