Age-Sex and Population Pyramids

The Most Useful Graphs in Population Geography

People stacked into a pyramid.

grendelkhan/Flickr/CC BY 2.0

The most important demographic characteristic of a population is its age-sex structure—the distribution of people's age and sex in a specific region. Age-sex pyramids (also known as population pyramids) graphically display this information to improve understanding and make comparison easy. When displaying a growing population, they sometimes have a distinctive pyramid-like shape.

How to Read an Age-Sex Graph

An age-sex pyramid breaks down a country's or location's population into male and female genders and age ranges. Usually, you'll find the left side of the pyramid graphing the male population and the right side of the pyramid displaying the female population.

Along the horizontal axis (x-axis) of a population pyramid, the graph displays the population number. It can represent a total population of that age—the total number of males/females who are of a certain age. Or, the number can stand for a percentage of the population at that age—how many percent of the entire population are of a certain age. The center of the pyramid starts at zero population and extends out to the left for males and right for females in increasing size or proportion of the population. 

Along the vertical axis (y-axis), age-sex pyramids display five-year age increments, from birth at the bottom to old age at the top.

Some Graphs Actually Look Like a Pyramid

Generally, when a population is growing steadily, the longest bars of the graph will appear at the bottom of the pyramid and will generally decrease in length as the top of the pyramid is reached. This indicates a large population of infants and children, which declines toward the top of the pyramid due to the death rate.

Age-sex pyramids graphically display long-term trends in the birth and death rates but also reflect shorter-term baby-booms, wars, and epidemics.

Three basic types of population pyramids show how different trends are displayed. 

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Rapid Growth

Afghanistan age-sex pyramid graph.
This age-sex pyramid for Afghanistan shows very rapid growth.

U.S. Census Bureau

This age-sex pyramid of Afghanistan's population breakdown in 2015 displays a fast growth rate of 2.3 percent annually, which represents a population doubling time of about 30 years.

We can see the distinctive pyramid-like shape to this graph, which displays a high birth rate. Afghan women have, on average, 5.3 children, the total fertility rate. But the country also has a high death rate, as life expectancy in Afghanistan from birth is only 50.9.

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Slow Growth

U.S. age-sex pyramid 2015.
This age-sex pyramid for the United States displays slow population growth.

U.S. Census Bureau

In the United States, the population is growing at a very slow rate of about 0.8 percent annually, which represents a population doubling time of almost 90 years. This growth rate is reflected in the more square-like structure of the pyramid.

The total fertility rate in the United States in 2015 was estimated at 2.0, which results in a natural decline in the population. A total fertility rate of about 2.1 is required for population stability. As of 2015, the only growth in the United States is from immigration.

On this age-sex pyramid, you can see that the number of people in their 20s of both genders is significantly higher than the number of infants and children aged 0-9. 

Also, note the lump in the pyramid between the ages of 50-59. This large segment of the population is the post-World War II baby boom. As this population ages and climbs up the pyramid, there will be a much greater demand for medical and other geriatric services. However, there are fewer young people to provide care and support for the aging baby boom generation.

Unlike the Afghanistan age-sex pyramid, the United States population shows a significant number of residents aged 80 and above, showing that increased longevity is much more likely in the U.S. than in Afghanistan. Note the disparity between male and female elderly in the United States. Women tend to outlive men in every population group. In the U.S., life expectancy for men is 77.3 but for women, it is 82.1.

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Negative Growth

Japan age-sex pyramid graph.
This age-sex pyramid for Japan shows negative population growth.

U.S. Census Bureau

 As of 2015, Japan has been experiencing a negative population growth rate of -0.2%, forecast to drop to -0.4% by 2025.

Japan's total fertility rate is 1.4, which is below the replacement rate necessary for a stable population of 2.1. As Japan's age-sex pyramid shows, the country has a huge number of elderly and middle-aged adults.

About 40 percent of Japan's population is expected to be over 65 by 2060, and the country is experiencing a dearth (or scarcity) in the number of babies and children. In fact, Japan has experienced a record low number of births since 2011.

Since 2005, Japan's population has been declining. In 2005, the population was 127.7 million and in 2015, it dropped to 126.9 million. The Japanese population is projected to hit 107 million by 2050, and if current predictions hold true, Japan will have a population under 43 million people by 2110. 

Japan has been taking its demographic situation seriously, but unless Japanese citizens start reproducing, the country will have a demographic emergency. 


  • Gygi, F. "Impact of Japan's Shrinking Population 'Already Palpable.'" Deutsche Welle, June 2015. 
  • Ghosh, P. "Japan Encourages Young People to Date and Mate to Reverse Birth Rate Plunge, but It May Be Too Late." International Business Times, New York, NY, March 21, 2014.
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Rosenberg, Matt. "Age-Sex and Population Pyramids." ThoughtCo, Apr. 5, 2023, Rosenberg, Matt. (2023, April 5). Age-Sex and Population Pyramids. Retrieved from Rosenberg, Matt. "Age-Sex and Population Pyramids." ThoughtCo. (accessed June 6, 2023).