Density is the number of things—which could be people, animals, plants, or objects—in a certain area


6 - 12+


Geography, Human Geography, Mathematics, Physics

NGS Resource Carousel Loading Logo
Loading ...
Powered by
Morgan Stanley

Density is the number of things—which could be people, animals, plants, or objects—in a certain area. To calculate density, you divide the number of objects by the measurement of the area.

The population density of a country is the number of people in that country divided by the area in square kilometers or miles. The country of Singapore is one of the most densely populated countries in the world. It has a population of 4,839,400 and an area of 687 square kilometers (265 square miles), so its density is 7,044 people per square kilometer (18,262 per square mile).

Of course, not all the people in the country are spread out evenly. Cities have a greater population density than rural areas.

Density can also be used to refer to the number of plants or animals in a certain area. Sometimes, animal or plant populations are too dense. This leads to overpopulation.

Deer have overpopulated areas of the Midwestern United States, for example. A common reason is a lower density of their natural predators, such as pumas or bears. As a result of the deer’s dense population, the competition for land and food is heightened and many deer die of starvation. Vegetation does not have time to develop, so food becomes scarce. A habitat can only support a limited number of each type of organism, so an overpopulation of deer can drive those deer to other habitats, including human habitats such as towns.

Density can refer to the number of molecules in a substance. This can apply to gases, liquids, and solids.

Air quality is defined by the number of pollutants in a certain area. Air quality therefore measures the density of air pollutants, such as smoke and emissions. Densely populated cities often have poor air quality because of the air pollution density.

Density is used to measure the salinity of seawater. Water densely packed with salt has a high salinity. Water that has few salt molecules has low salinity.

Rocks and minerals are also measured for density. Many igneous rocks, or rocks formed from volcanic eruptions, have a low density. They are full of pockets of air. One type of igneous rock, pumice, has such a low density that it can actually float on water. The water is more dense than the rock.

Fast Fact

Elbow Room in Africa
Namibia, one of the least densely populated countries in the world, has just 2.6 people per square kilometer (6.6 per square mile.)

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Kim Rutledge
Melissa McDaniel
Santani Teng
Hilary Hall
Tara Ramroop
Erin Sprout
Jeff Hunt
Diane Boudreau
Hilary Costa
Mary Crooks, National Geographic Society
Tim Gunther
Jeannie Evers, Emdash Editing, Emdash Editing
Kara West
Educator Reviewer
Nancy Wynne
National Geographic Society
Last Updated

October 19, 2023

For information on user permissions, please read our Terms of Service. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. They will best know the preferred format. When you reach out to them, you will need the page title, URL, and the date you accessed the resource.


If a media asset is downloadable, a download button appears in the corner of the media viewer. If no button appears, you cannot download or save the media.


Text on this page is printable and can be used according to our Terms of Service.


Any interactives on this page can only be played while you are visiting our website. You cannot download interactives.

Related Resources