Population pyramid
A chart of how many people are in each age group, split by sex, stacked from youngest to oldest.
In short
A pyramid is really two bar charts placed back to back, one for each sex, arranged so the whole shape shows how a population is built up by age.
How to read one
Each row is a five-year age band, youngest at the bottom. The length of each side shows how many people of that sex fall into that band. The overall outline, not any single bar, is what tells the story.
Males are conventionally shown on the left, females on the right. The horizontal axis shows either the raw count or the percentage of the total population. Percentage makes it easier to compare countries of different sizes.
Typical shapes
Why it matters here
A pyramid is the shape that dependency ratio and median age are both trying to summarise into a single number. This site doesn't show full pyramids yet: the preview on the Components page is a placeholder for a later release. Underneath, though, every ridgeline is built from age bands like these.
The pyramid shape at any moment is the accumulated result of past fertility, mortality, and migration. A baby boom shows up as a bulge that moves upward through the pyramid over decades. A war or famine cuts a notch that persists for generations. Reading a pyramid well means reading a country's demographic history. The UN's interactive population pyramids let you step through any country's age structure from 1950 to 2100.
How shapes change over time
As a country moves through the demographic transition — from high fertility and high mortality to low fertility and low mortality — its pyramid changes predictably. The base first widens as child survival improves (more children survive, so each cohort is larger), then narrows as fertility falls. The middle fills out as those large cohorts age into adulthood, and the top grows as life expectancy lengthens. The sequence from true pyramid to rectangle to inverted shape typically takes two to four generations.
Frequently asked questions
What is a population pyramid?
A population pyramid is a graphical representation of a population's age and sex structure. It consists of two back-to-back horizontal bar charts — one for males on the left and one for females on the right — with each bar representing a five-year age group, arranged from youngest at the bottom to oldest at the top. Our World in Data's age structure page lets you compare pyramids across countries and years interactively.
What does a wide base on a population pyramid mean?
A wide base means there are many young people relative to older age groups — a sign of high recent fertility and a fast-growing population. Countries in sub-Saharan Africa typically show this shape today. As fertility falls over time, the base narrows and the pyramid gradually takes on a more rectangular or even top-heavy shape. PopulationPyramid.net provides interactive pyramids for every country from 1950 to 2100.
What does an ageing population pyramid look like?
An ageing population pyramid has a narrower base and a bulge in the middle or upper age bands. This reflects years of declining fertility (fewer births) combined with rising life expectancy. Japan, Germany, and Italy are examples of countries with this inverted or barrel-shaped pyramid structure. The UN World Population Ageing 2023 report analyses trends and projections for older populations in depth.
How does a population pyramid relate to the dependency ratio?
The dependency ratio is essentially a single number derived from the shape of the population pyramid: the combined size of the bars at the bottom (children, 0–14) and the top (older adults, 65+) relative to the bars in the middle (working-age adults, 15–64). A pyramid with a wide base has a high youth dependency ratio; one with a narrow base and wide top has a high old-age dependency ratio.