What is acre?
An acre is a unit of area in imperial and US customary systems equal to 43,560 square feet. It is the standard unit for measuring agricultural land, property lots, and parks in the United States and United Kingdom.
Real-world uses
Acres are used for land parcels, farm sizes, and real estate in the US, UK, and some Commonwealth countries. Zoning laws often specify minimum lot sizes in acres. An American football field (including end zones) is about 1.32 acres.
History
The acre originated in medieval England as the amount of land a yoke of oxen could plough in one day. The word comes from Old English "æcer." It was standardized as a strip 1 furlong (660 ft) by 1 chain (66 ft), yielding 43,560 square feet.
Common mistakes
Assuming an acre is a square measure with specific dimensions—it is 43,560 sq ft but can be any shape. Also, confusing acres with hectares: 1 acre ≈ 0.405 hectares, so roughly 2.5 acres make one hectare.
What is square mile?
A square mile is a unit of area in imperial and US customary systems equal to 640 acres. It is used to express the size of cities, regions, and geographic territories in the United States and United Kingdom.
Real-world uses
Square miles are used for city areas, county sizes, and population density calculations in the US and UK. Manhattan is about 23 square miles. National parks and wilderness areas are often described in square miles in American contexts.
History
The square mile became a standard geographic unit in English-speaking countries alongside the statute mile. The US Public Land Survey System, established in 1785, divided territory into 36-square-mile townships, each containing 36 one-square-mile sections.
Common mistakes
Assuming 1 square mile = 1 mile × 1 mile = 1 mi². While correct, people forget that 1 sq mi = 640 acres or about 2.59 km², leading to errors when comparing American and metric area figures.
When is this conversion used?
Converting acre to square mile is useful in the area domain when comparing values across different measurement standards or applying formulas that require a specific unit.
Worked examples
1 acre = 0.0015625 square mile
1 square mile = 2,589,988.110336 square metre
How to convert acre to square mile
To convert acre to square mile, multiply the value by 0.0015625.
To convert square mile back to acre, multiply by 640.
Measurement standards
The square metre is the SI derived unit of area. The hectare (10,000 m²) is accepted for use with the SI by the BIPM, particularly for land measurement, though it is not an SI unit itself.
Did you know?
Vatican City, the world's smallest independent state, covers just 0.44 km² (about 109 acres) — smaller than many golf courses. By contrast, Russia spans over 17.1 million km², nearly 39 million times larger.
Quick reference: acre to square mile
| acre | square mile |
|---|---|
| 0.1 | 0.00015625 |
| 0.5 | 0.00078125 |
| 1 | 0.0015625 |
| 2 | 0.003125 |
| 5 | 0.0078125 |
| 10 | 0.015625 |
| 25 | 0.0390625 |
| 50 | 0.078125 |
| 100 | 0.15625 |
| 250 | 0.390625 |
| 500 | 0.78125 |
| 1,000 | 1.5625 |
Common values
| acre | square mile | |
|---|---|---|
| A4 paper | 0.00001532 acre | 2.393833e-08 square mile |
| Parking space | 0.00308882 acre | 0.00000483 square mile |
| Tennis court | 0.06446238 acre | 0.00010072 square mile |
| Football field (soccer) | 1.76433242 acre | 0.00275677 square mile |
| Central Park, NYC | 842.6293508 acre | 1.31660836 square mile |