Population Density Calculator

What population density measures

Population density answers one question: if the people of a place were spread evenly across its land, how many would stand on each unit of ground? Divide the population by the land area and the result is an average, expressed as people per square mile in the United States and people per square kilometer in most other countries.

The number is an average, and averages hide shape. The 2020 Census put the United States at 93.8 people per square mile of land, yet almost nobody lives at that spacing. People cluster into metropolitan areas and leave farmland, desert and forest thinly settled. Density still earns its place because it compresses a population and an area into one comparable figure, and because a family of practical estimates hangs off it: school seats, water demand, housing units, transit routes and emergency service coverage all get sized per resident, and density tells you how many residents sit on a given piece of ground.

The calculator on this page runs the division in every common unit at once. Enter a population and an area, pick the unit the area is already in, and you get people per square mile, per square kilometer, per acre and per hectare, plus the reverse measure of acres per person.

The formula and the units that go into it

Density = population / land area. That is the whole calculation. The work sits in the units, because an area in acres and a population in thousands produce a number that means nothing until you say what it is per.

Any area unit works as long as you name it, and the conversions between the common ones are fixed:

The conversion that trips people is miles to kilometers for an area. A mile is 1.609 kilometers, so a square mile is 1.609 x 1.609 = 2.589988 square kilometers, not 1.609. Density in people per square kilometer is therefore smaller than density in people per square mile by that same factor: the United States at 93.8 per square mile is 36.2 per square kilometer.

An acre is the unit that catches American land listings, and it is small enough to make suburban densities sound large. There are 640 acres in a square mile, so 1,000 people per square mile is 1.5625 people per acre. A hectare is 10,000 square meters, roughly 2.47 acres, which is why European densities reported per hectare look about two and a half times larger than the same density per acre.

Land area, not total area

The Census Bureau defines population density as the average population per square mile of land, and the word land is doing real work. Lakes, rivers, reservoirs and coastal water are excluded from the area figure, so density counts only the ground people can stand on.

For the country as a whole the difference is small, a few percent. For a place with a Great Lake on its border or a wide river through its middle, it can move the answer noticeably. Use total surface area and a waterside city looks less dense than it is; use land area and the number describes the space residents share.

The same choice appears at every scale. A county's land area comes from the Census Bureau's area measurements, a city's from its official boundary file, and a parcel's from the deed. Whatever you pick, state it, because two people comparing densities computed on different area bases will argue about a difference that comes from the map rather than the population.

Boundaries change too. A city that annexes farmland adds area and population at once, and the new density depends on which grew faster. When a number looks surprising, check the boundary year before doubting the arithmetic.

Worked example: 8,000 people on 4 square miles

A town of 8,000 residents covers 4 square miles of land. That is 8,000 / 4 = 2,000 people per square mile, and the table converts the same fact into the other units.

Read against the national figure, this town is 21 times as dense as the United States average of 93.8, and denser than New Jersey, the most crowded state at 1,263.0 per square mile. In land per person terms, each resident accounts for 0.32 acres, which is 0.32 x 43,560 = 13,939 square feet, roughly a third of an acre or a plot about 118 feet on a side.

That last comparison is the one worth keeping. Density numbers sound abstract until they become land per person, and land per person is what planning arguments are about: a school site, a parking requirement, a septic field, a fire station's response radius. The same 2,000 per square mile can describe a compact village surrounded by fields or a uniform grid of quarter-acre lots, and the arithmetic cannot tell them apart.

How the United States compares

The 2020 Census counted 331,449,281 residents in the 50 states and the District of Columbia, spread over about 3.53 million square miles of land. The table below shows what that produces at the national level and in a spread of states, using the Census Bureau's own density figures.

New Jersey is the most densely settled state, and the District of Columbia outranks it several times over at 11,280.0 per square mile, about 120 times the national figure. Alaska sits at the other end with 1.3, so the spread between the top and bottom of the list is close to four orders of magnitude. Texas, often pictured as open country, comes in above the national average because its population is concentrated in a handful of metro areas while its land area is large but not empty.

These are decennial counts, not estimates, and they are the figures the Census Bureau publishes for density. The historical density table carries every state back to 1910, which makes it easy to see the long climb: the national figure was 26.0 in 1910, 57.5 in 1970 and 93.8 in 2020.

The reverse reading: acres per person

Density and land per person are the same measurement upside down. Divide 640 acres by the density in people per square mile and you get acres per person: 640 / 93.8 = 6.82 for the United States as a whole, and 640 / 2,000 = 0.32 for the example town.

The inverse form is handy for planning because it scales linearly with what you are trying to place. At 2,000 people per square mile, a 1,000-home subdivision at 2.5 people per home needs 2,500 people, which needs 1.25 square miles of land at that density. Multiply or divide and the answer follows without touching a map.

It also makes international comparisons easier to feel. A country reported at 36 people per square kilometer gives each resident about 2.8 hectares, which is 6.9 acres. The arithmetic is unglamorous, but it turns a headline number into something you can picture: a house lot, a farm field, a park.

One caution: land per person is an average over everyone, including the people who live in apartments and the land that grows the food those apartment dwellers eat. It is not a measure of anybody's actual yard.

Five mistakes that skew the number

Dividing by total area instead of land area. Water counts in the first and not the second, and the Census convention is land. Using total area understates density wherever lakes or coastline take up space.

Using the length conversion for an area. A kilometer is 1.609 miles, but a square kilometer is 0.386 square miles. Dividing a density by 1.609 instead of 2.589988 produces a number that is too large by about 61 percent.

Reading density as a population. A density of 2,000 per square mile says nothing about how many people live there. Ten square miles at that density is 20,000 people; one square mile is 2,000.

Mixing years. Pairing a 2024 population estimate with a 2010 boundary, or a 2020 count with a current annexation, produces a figure that belongs to no single moment. State the year of each input.

Forgetting that the average hides clustering. A rural county and a dense town can share a density of 100 per square mile while feeling nothing alike. If the question is about crowding, walkability or service delivery, density alone will not answer it, and a distribution or a map is needed.

Where to get populations and areas you can trust

For the United States, the decennial census is the anchor. The 2020 count is the most recent complete enumeration, and the Census Bureau publishes density directly for states, counties and places, along with the land area used. The 2020 density table lists every state and Puerto Rico with population, density and rank, and the accompanying notes state the land area convention.

For countries, the World Bank population density indicator reports people per square kilometer of land area, drawing on FAO and World Bank population estimates, with a series running from 1961 to 2024. Because it uses land area and square kilometers, its figures will not match a source that divides by total area or reports per square mile. Converting is simple: divide by 2.589988 to go from per square mile to per square kilometer.

Between censuses, population estimates are the practical source, and they are revised. A density computed from a vintage 2023 estimate and a 2020 land area is a reasonable working number, as long as the page or report says which vintage it used. Land area changes slowly, through annexation and better measurement, so it is usually the stable input in the pair.

Every figure on this page comes from the 2020 Census. When the 2030 counts are published, the national density, the state rankings and the worked comparisons here will need to be replaced rather than adjusted.