# What is the population density?

Divides a population by its land area to give the population density in people per square mile and per square kilometer, from an area in any common unit.

- Page: https://www.acalculator.org/everyday-life/population-density-calculator
- JSON spec: https://www.acalculator.org/everyday-life/population-density-calculator.json
- Version: 81a8686c8edf

## Default answer

Example with the default inputs (Population 331,449,281, Land area 3,533,038.28, Area unit Square miles): The population density is 93.81 people per square mile (36.22 per square kilometer).

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| pop | Population | The number of people living in the place. |
| area | Land area | The land area of the place, in the unit below. Water is usually left out. |
| u | Area unit | The unit the land area is typed in. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| perMi2 | People per square mile | Population ÷ land area in square miles. |
| perKm2 | People per square kilometer | Population ÷ land area in square kilometers. |
| perAcre | People per acre | Population ÷ land area in acres. |
| areaKm2 | Land area in square kilometers | The typed area converted to square kilometers. |
| areaMi2 | Land area in square miles | The typed area converted to square miles. |

## Method

Density = population ÷ land area. Area is converted exactly: 1 sq mi = 2.589988110336 km², 1 acre = 0.0040468564224 km², 1 hectare = 0.01 km².

## Assumptions

- The area is land area, as the Census Bureau uses; include water only if you mean to.
- You type both numbers; the page looks up no data.

## Worked examples

1. pop = 331,449,281, area = 3,533,038.28, u = mi2 gives perMi2 = 93.814234, perKm2 = 36.221878. Source: US Census Bureau QuickFacts, United States: population April 1, 2020 331,449,281; https://www.census.gov/quickfacts/note/POP060220.
2. pop = 1,000,000, area = 250, u = km2 gives perKm2 = 4,000, perMi2 = 10,359.952441, areaMi2 = 96.52554. Source: https://www.census.gov/quickfacts/note/POP060220.
3. pop = 500, area = 200, u = acre gives perAcre = 2.5, perMi2 = 1,600. Source: https://www.census.gov/quickfacts/note/POP060220.

## FAQ

### How do I calculate population density?

Divide the population by the land area. The United States had 331,449,281 people on 3,533,038.28 square miles of land in 2020: 331,449,281 ÷ 3,533,038.28 = 93.8 people per square mile.

### How do I convert people per square mile to people per square kilometer?

Divide by 2.589988110336, the number of square kilometers in a square mile (or multiply by about 0.3861, as the Census Bureau notes). 93.81 per square mile is 36.22 per square kilometer.

### Should I use total area or land area?

The US Census Bureau divides by land area, which leaves out lakes, rivers, coastal water and territorial seas. Using total area gives a lower density for places with a lot of water.

### What is a high population density?

It depends on the scale. In 2020 the United States as a whole had about 94 people per square mile, while a dense city can have tens of thousands. Compare places of the same kind, such as counties with counties.

### Why do two sources give different densities for the same place?

They may use a different population year, a different area (land or total), or a different boundary, such as a city limit or a metro area. Check all three before comparing.

## Sources

- US Census Bureau. QuickFacts note: Land Area and Persons Per Square Mile (density is the population divided by the land area in square miles or square kilometers), retrieved 2026-10-18. https://www.census.gov/quickfacts/note/POP060220
- US Census Bureau. QuickFacts, United States (population April 1, 2020; land area in square miles, 2020; population per square mile, 2020), retrieved 2026-10-18. https://www.census.gov/quickfacts/fact/table/US/POP060220
- NIST. Special Publication 811, Guide for the Use of the International System of Units, Appendix B.8 (foot, mile, square mile, hectare), retrieved 2026-10-18. https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8