# Population Growth Rate: Definition, Formula & Examples

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• 0:03 Changes in Population
• 0:51 Formula for Population Change
• 1:44 Example One
• 3:02 Example Two
• 4:09 Lesson Summary

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Lesson Transcript
Instructor: Lauren Posey

Lauren has taught intermediate reading in an English Language Institute, and she has her Master's degree in Linguistics.

Population growth rate is an important factor to consider when looking at the past and future of a population. In this lesson, you'll learn how to calculate the growth rate.

## Change in Population

Think about the town where you live. How long have you lived there? Do you know how much that town has grown since you've been there? If you determine the overall amount the population has changed in the entire time you've been there, this only tells you the change in population size. However, this doesn't really help you think about annual growth or predict future growth for your town. To do this, you need to know the population growth rate.

The population growth rate expresses the change in population size as a factor of time. Typically, both for human and non-human populations, we want to know the average annual growth rate. This gives us more information than stating the exact population growth for the entire time period, and allows us to better predict future years of growth or decline for the population.

## Formula for Population Change

The standard formula for calculating growth rate is:

Gr= N / t

Here, Gr is the growth rate expressed as a number of individuals. N is the total change in population size for the entire time period, also expressed as a number of individuals. t is time, usually expressed in number of years. Of course, for really quickly growing populations, it might also be expressed in months or some other unit of time. The formula is calculated the same way regardless of the unit of time used.

In order to calculate the overall growth rate, you first have to figure out N. This is done by subtracting the initial population (or P1) from the current population, or the population at the end of the time period you are using (or P2). Therefore:

N= P2 - P1

Now, let's take a look at few examples that put this formula into practice.

## Example One

You are looking into the history of your town, and you'd like to know exactly how much the population has grown since 1980. Town records have kept track of the overall population each year. The current population for 2017 is 300,000 people. Back in 1980, the population was only 150,000 people.

First, you need to determine N, the overall change in population size since 1980:

N= 300,000 - 150,000

So, the total change in population size since 1980 is 150,000 people.

Next, you need to determine the number of years by subtracting the end year from the start year:

2017 - 1980 = 37

So, t=37.

Now you can plug all of this information into the formula:

Gr=150,000 / 37

So,

Gr= approximately 4,054

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