How to read a population pyramid
A population pyramid shows how many people there are at each age: men on the left, women on the right, the youngest at the bottom. A wide base means many children, a wide top many older people.
The parts
- The vertical axis is age, from 0 at the bottom to 100 and over at the top. On Anthrotempo each bar is one year of age.
- The horizontal axis is the number of people. Men are drawn to the left of the centre line, women to the right.
- Each bar is everyone of that age on the reference date, here 1 January.
What the shape tells you
A broad base that narrows quickly belongs to a young, fast-growing population: many children, fewer people at each older age. Niger has one of the youngest populations in the data.
A narrow base and a wide middle or top belongs to an older population with few births. Japan is an example: its pyramid is narrower at the bottom than in the middle.
Bulges and notches follow a group of people through life. A bulge is a large birth cohort, a notch a small one: years with fewer births, or losses in a war. As the years pass, each bulge moves up the pyramid by one year of age per year.
Reading it carefully
- Compare shapes, not only sizes: countries of very different size can have the same shape. The pyramid tool can show shares of the population instead of counts.
- At the top, women usually outnumber men, because women live longer on average.
- The top bar, 100 and over, is an open group: it holds everyone from 100 up, so it is not one year wide.
- For years from 2024 on, the pyramid is a UN projection and is marked as one.
Last updated 26 October 2026