Convert mi² to acres square miles ↔ acres Free Online Secure
Type a value in square miles and read it in acres at once. The factor is exact by definition, the arithmetic happens in your browser, and nothing is sent anywhere.
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Common values — Convert mi² to acres (square miles ↔ acres)
| mi² | ac |
|---|---|
| 1 | 640 |
| 2 | 1280 |
| 3 | 1920 |
| 5 | 3200 |
| 10 | 6400 |
| 20 | 12800 |
| 50 | 32000 |
| 100 | 64000 |
Where these units come from
Square units need no definition of their own: a square metre is a metre by a metre, and everything follows from the length. The land measures are older and stranger. The acre began as the land a yoke of oxen could plough in a day, which is why it was long and thin rather than square — one chain by one furlong, 4840 square yards. The hectare and the are came out of the French Revolution, when land had to be measured in something decimal; neither belongs to the International System, but both were kept for land because a hectare is a comfortable size to picture and a square metre is not. Since the 1959 agreement on the yard, the acre is exactly 4046.8564224 square metres, so the conversions on this page are exact rather than approximate.
Where you meet them
Square metres price flats, size carpets and decide how much paint a wall needs; square feet do the same work in the United States and in much of the property market worldwide. Hectares belong to farmland, forests and planning permissions; acres to land deeds in the English-speaking world. Square kilometres and square miles are for countries, lakes and fires. Square centimetres and square millimetres live in workshops, on datasheets and anywhere a cross-section matters.
Questions people ask
How many acres are in a square mile?
640 acres, and a square mile is exactly 2.589988110336 square kilometres. American land surveys divided territory into sections of one square mile, which is why 640 acres is such a recognisable figure. For larger regions the square kilometre is more convenient.
Is an acre the same in the United States?
For every practical purpose, yes. The international acre used here is exactly 4046.8564224 m². The United States also kept a survey acre, based on a slightly different foot, which was larger by about four parts in a million — a difference of some 160 cm² in an acre, invisible except in large land surveys. That survey foot was formally retired at the end of 2022, so only one acre is now in use.
Is the answer exact?
Where both units are defined in terms of one another by whole numbers, yes — the page says so above the figure, and the only rounding is in how many digits are shown. Where the ratio has no finite decimal, the page shows twelve significant digits and says the relation is approximate rather than pretending otherwise.
Does anything I type leave my device?
No. The arithmetic runs in your browser; nothing is uploaded and there is no server to upload it to. Load the page once and it keeps working with the network switched off.
Public lands, cropland and lawns: the American continent in acres
National land statistics in the United States are published in acres: the federal estate is 640 million acres, farmland nearly 900 million, lawns about 40 million. Atlases and journalists, however, often turn the figures into square miles to give a sense of scale. To convert mi² to acres you multiply by 640, because a square mile is exactly 640 acres. So 1,000 mi² is 640,000 acres, and 30,000 mi² is 19.2 million. This page multiplies as you type, and the text below explains how the big national totals look in each unit.
Below come the rule, some worked cases, a brief look at each unit, a side by side comparison, a tour of national land statistics and the slips to avoid. Everything is computed on your own device while you type.
How to convert mi² to acres: multiply by 640
The rule
One square mile is exactly 640 acres. To convert mi² to acres, multiply the square miles by 640. So 0.25 mi² is 160 acres, 3 mi² is 1,920 acres, 50 mi² is 32,000 acres and 1,000 mi² is 640,000 acres. To go back, divide acres by 640.
Worked examples
The Arctic National Wildlife Refuge has about 30,000 mi², which is 19.2 million acres. Yellowstone has 3,472 mi², 2.22 million acres. A county of 1,100 mi² has 704,000 acres. When the square mile figure has decimals, multiply as usual: 0.3125 mi² is 200 acres.
Why 640
A mile is 8 furlongs and an acre is a furlong by a chain, so a square mile holds 8 by 8 furlong squares, 64, and each of them has 10 acres. The factor is built into the English system of land measure, designed so that its units fit together neatly.
A quick check
The acre is the small unit, so the number grows by hundreds. If your “convert mi² to acres” calculation gave you fewer acres than the square miles you began with, you divided instead of multiplying.
The square mile
One mile on a side
The square mile is 2.59 km², 259 hectares or 640 acres. It is the usual unit for states, counties, cities, parks and refuges in the United States and Britain. Population density is quoted per square mile.
Where it appears
Census publications, almanacs, news about disasters, aviation charts and encyclopaedias.
The acre
A furlong by a chain
The acre is 4,046.86 m², 43,560 ft², or 4,840 yd². It began as the day's ploughing of a pair of oxen, and survives as the standard unit of rural land in the English speaking world. A section of land is 640 acres, a quarter section 160.
Where it appears
Deeds, farm sales, public land statistics, conservation easements and national totals of land use.
Square mile and acre compared
A square mile holds 640 acres. Large areas are naturally given in square miles, and parcels in acres, but national totals sit in between: 893 million acres of farmland is 1.4 million square miles. The same number looks vast in acres and modest in square miles, which is why news reports switch units to suit their story.
The factor, 640, is exact and easy to remember. The mistake to avoid is mixing up miles and square miles, or using 1,760, the number of yards in a mile, instead of 640.
Where the conversion appears
Federal public lands
The Bureau of Land Management administers about 245 million acres, 383,000 mi². The Forest Service manages 193 million acres, 301,000 mi². The Fish and Wildlife Service has about 150 million acres in refuges, 234,000 mi². Together the federal estate is nearly 640 million acres, a million square miles, about 28 per cent of the country. A “convert mi² to acres” calculation puts each agency's figure in the unit you prefer.
Agriculture
American farmland covers about 893 million acres, 1.4 million square miles. Corn takes about 90 million acres, 140,600 mi², and wheat 47 million, 73,400 mi². The Department of Agriculture publishes acres, and the Census Bureau square miles for the states, so national comparisons need a conversion.
Lawns and golf
American lawns cover about 40 million acres, 62,500 mi², larger than the state of Georgia's land area. Golf courses use about 2 million acres, 3,100 mi². Studies of water and fertiliser use start from the acreage and compare with state areas in square miles.
The Alaska Purchase
In 1867, the United States bought Alaska from Russia, 586,412 mi², 375 million acres, for 7.2 million dollars, about 1.9 cents an acre. Today the state is 665,384 mi² including water, 426 million acres. The story is a standard one in textbooks, which give the area in square miles, while the price per acre is calculated in cents.
Timberland and forestry
Commercial timberland in the United States covers about 514 million acres, 803,000 mi². Maine, the most forested state, has 17.6 million acres, 27,500 mi². Forestry inventories report acres, and a map of a state's forest cover in square miles requires a “convert mi² to acres” calculation.
Military installations
The Department of Defense holds about 27 million acres, 42,000 mi², in the United States, an area the size of Kentucky. White Sands Missile Range covers 2.2 million acres, 3,400 mi². Defence reports give acres, and discussions of their impact on the environment mention square miles.
Mining claims
An American lode claim is 20 acres, and a placer claim up to 160 acres, a quarter of a section. A block of 32 claims has 640 acres, one square mile. Mining companies report claims in acres, and maps show the holding in square miles.
Hunting leases and ranches
A Texas hunting lease of 3,200 acres is 5 mi², and a ranch of 100,000 acres 156 mi². The King Ranch has 825,000 acres, 1,289 mi². Brokers quote acres, and readers who want a picture of the size convert to square miles, or compare with a county.
Wetlands and conservation
The United States has about 110 million acres of wetlands, 172,000 mi², about 5 per cent of the area of the lower 48 states. Programmes that restore wetlands count acres restored per year. A “convert mi² to acres” calculation turns annual targets into area on a map.
Cemeteries and memorial parks
Arlington National Cemetery covers 639 acres, almost exactly one square mile, 0.998 mi². Forest Lawn in Glendale has 300 acres, 0.47 mi². Cemetery sizes are given in acres in the United States, and the near coincidence of Arlington with a square mile makes a good memory aid for the factor 640.
Fire perimeters and burned area
Large wildfires are measured in acres by fire agencies. A fire of 400,000 acres is 625 mi². A season in which 10 million acres burn, 15,625 mi², is a bad one. Reports from firefighters use acres, and the press uses square miles to make a comparison with a county or a city.
Spreadsheet use
Write square miles in column A and =A2*640 in column B. For the reverse, use =B2/640. Format with no decimals. A third column with =A2*2.58999 gives square kilometres. Totals at the bottom allow comparisons with the state or country.
Rounding
The factor 640 is exact, so rounding is only for presentation. For national totals, give millions of acres with one decimal. For counties, give thousands. Do not invent digits: 3,472 mi² is 2,222,080 acres, but the figure is better quoted as 2.2 million.
Teaching the idea
Draw a square on the board and divide it into 8 by 8 small squares. Say that each small square is a furlong squared, 10 acres. Students count 64 squares, multiply by 10, and arrive at 640. They then test with a quarter, 16 squares, 160 acres, the size of a homestead.
The Homestead Act's legacy
Between 1862 and 1934, about 270 million acres, 422,000 mi², were claimed under the Homestead Acts, about 10 per cent of the country. A claim was 160 acres, a quarter of a square mile. Historians count homesteads and acres, and map them in square miles, so a “convert mi² to acres” calculation is part of the work.
A picture of an acre in a square mile
Imagine a square mile as a chessboard of 640 squares, one acre each. A section of land drawn on a map has the same layout. A quarter section is 16 by 10 squares. This picture helps you to estimate the answer to a “convert mi² to acres” calculation before you calculate it, and to notice when a result is out by a large factor.
Rivers, reservoirs and dams
The Bureau of Reclamation manages reservoirs covering about 1.5 million acres, 2,300 mi². Lake Powell alone holds 163,000 acres, 254 mi², when full. Water managers speak in acre feet for volume and acres for surface, while maps show square miles, so a “convert mi² to acres” calculation is routine in hydrology reports from the American West.
Railroads and rights of way
The American railroad network of 140,000 miles, with a right of way of 100 feet, covers about 1.7 million acres, 2,650 mi². Pipeline and power line corridors add another 4 million acres, 6,250 mi². Utilities and regulators publish rights of way in acres, and the press translates them into square miles for readers.
Suburbs and subdivisions
A subdivision of 1 mi², 640 acres, with 3 homes per acre holds 1,920 houses, while one of 0.5 acre lots holds only 1,000 after roads. Developers think in acres per house, planners in square miles per jurisdiction. The conversion is part of every density debate in a county board meeting.
Spaceflight and launch ranges
The Kennedy Space Center covers 140,000 acres, 219 mi². Vandenberg Space Force Base has 99,600 acres, 156 mi². Launch ranges use acres for their land holdings and square miles for the hazard areas around the pad, so a conversion is a common step in safety studies.
A list of anchors to remember
A square mile is 640 acres, a half is 320, a quarter 160, an eighth 80, a sixteenth 40. Ten square miles are 6,400 acres, and a hundred are 64,000. Between those anchors you can interpolate by eye. A glance at the list tells you at once whether a figure from a “convert mi² to acres” calculation is believable, and it protects against a slipped zero in a table that many people will read.
Why national totals are given twice
Government agencies publish acres because their records come from deeds and surveys, while geographers and newspapers prefer square miles because the numbers are shorter and compare easily with states and countries. A careful reader who meets both in one article should not be surprised: they describe the same land. Keep the factor 640 in mind and convert whichever figure you need.
Section numbers on a county map
On a map of a Midwestern county, the sections are numbered from 1 to 36 in a snake pattern, and each is labelled with its acreage, usually 640. Where the survey meets a river or a state line, a section may be smaller, say 412 acres, 0.64 mi². Reading such a map with a “convert mi² to acres” calculation in mind lets you check a landowner's claim against the grid without any special software.
National wildlife refuges
The Arctic National Wildlife Refuge covers 19.3 million acres, 30,000 mi². The Yukon Delta refuge has 19.1 million acres. The smallest refuge, Pelican Island, has 5,400 acres, 8.4 mi². The Fish and Wildlife Service gives acres, and the media often convert to square miles to compare with a state.
National parks of the United States
Wrangell St Elias has 13.2 million acres, 20,600 mi². Death Valley 3.4 million acres, 5,300 mi². Grand Canyon 1.2 million acres, 1,900 mi². Great Smoky Mountains 522,000 acres, 816 mi². The National Park Service publishes acres, and the lists in guides show square miles, so a conversion helps when you compare parks.
Cropland by crop
The United States plants about 90 million acres of corn, 83 million of soybeans, 47 million of wheat and 11 million of cotton. In square miles that is 140,600, 129,700, 73,400 and 17,200. Crop reports publish acres planted and harvested, and a “convert mi² to acres” calculation turns them into a map friendly unit.
Urban land and sprawl
Developed land in the contiguous United States covers about 113 million acres, 177,000 mi², approximately 6 per cent of the area. Urban areas proper, the built up cores of cities, cover about 3 per cent of the country. Land use studies state acres, and urban geographers square miles.
Conservation easements and land trusts
American land trusts protect over 60 million acres, 94,000 mi², through easements. A single easement of 3,200 acres is 5 mi². Trusts report acres to donors, and public reports sometimes use square miles to compare with counties.
Irrigated land in the West
The United States irrigates about 58 million acres, 90,600 mi², about the area of Indiana and Illinois together. California has about 8 million acres under irrigation, 12,500 mi². Water agencies give acres for fields and acre feet for volume, and a conversion links them to maps in square miles.
Indian reservations
The Navajo Nation has 17.5 million acres, 27,400 mi². Federal reservations in total hold about 56 million acres, 87,500 mi². Legal documents use acres, while news reports use square miles when they want to compare reservations with states.
More values for convert mi² to acres
A longer list of conversions
If the value you need is not in the first list, these further conversions may be close enough to read off directly:
- 0.1 mi² = 64 ac
- 0.5 mi² = 320 ac
- 3 mi² = 1,920 ac
- 4 mi² = 2,560 ac
- 7 mi² = 4,480 ac
- 15 mi² = 9,600 ac
- 20 mi² = 12,800 ac
- 75 mi² = 48,000 ac
- 200 mi² = 128,000 ac
- 500 mi² = 320,000 ac
- 2,000 mi² = 1,280,000 ac
- 10,000 mi² = 6,400,000 ac
Mistakes when you convert mi² to acres
Dividing instead of multiplying
The acre is the small unit, so the number grows. If 10 mi² became 0.0156, you divided.
Using 1,760
That is the number of yards in a mile. For area, the factor is 640.
Mixing miles and square miles
Ten square miles is not a line of ten miles. Check that the figure is an area before converting.
Quick answers
How many acres in a square mile?
640.
How do I convert mi² to acres?
Multiply by 640.
How many square miles in an acre?
0.0015625.
What is 5 mi² in acres?
3,200 acres.
Is my number sent anywhere?
No, it stays in your browser.
Related pages and a last word
If you work with land and area, these conversions are close at hand: Convert mi² to km², Convert m² to acres, Convert ha to acres, Convert acres to ft², Convert km to mi, Convert mi to km, Convert °C to °F, Convert °F to °C, Convert L/min to m³/h. The reverse of this page is Convert acres to mi².
To sum up: multiply by 640 to convert mi² to acres, remember that a section is one square mile, and write the unit beside the result. The figure you enter is processed locally, with no account and no upload.