A country can have many people and still feel empty, or few people and feel crowded. To compare, we use population density: the number of people per square kilometer. It is a unit rate, like those in Unit Rates, built from a country's population and its area.
Key idea
Population density = people ÷ land area. The answer is in people per square kilometer (people per km²).
Why it works
Dividing shares the people out evenly: if 600 people live on 3 km², and they spread out evenly, each square kilometer has 600 ÷ 3 = 200 people. Real people are never spread evenly, so density is an average. It lets us compare a giant country and a tiny one fairly.
Worked example: An island
An island has 12,000 people on 40 km² of land. What is its population density?
- Density = people ÷ area.
- 12,000 ÷ 40 = 300.
Answer: 300 people per km².
Worked example: Many people, but less crowded
Bangladesh has about 174 million people on about 148,000 km². The United States has about 345 million on about 9.8 million km². Which is more crowded?
- Bangladesh: 174,000,000 ÷ 148,000 ≈ 1,200 people per km².
- United States: 345,000,000 ÷ 9,800,000 ≈ 35 people per km².
- Bangladesh has half as many people but is more than 30 times as crowded.
Answer: Bangladesh.
| Country | People per km² (about) |
|---|---|
| Monaco | 19,000 |
| Singapore | 8,000 |
| Bangladesh | 1,200 |
| India | 440 |
| United States | 35 |
| Australia | 3 |
| Mongolia | 2 |
Common mistake
A large population is not the same as a high density. Bangladesh has fewer people than the United States, but it is far more crowded, because they share much less land. Always divide by the area before you compare.