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 kilometre?
A square kilometre is a metric unit of area equal to one million square metres. It is used for measuring large geographic areas such as countries, forests, lakes, and urban zones.
Real-world uses
Square kilometres are used for country areas, city boundaries, national park sizes, and deforestation tracking. Geographic and environmental data, including satellite imagery resolution, reference areas in km². Singapore is about 733 km², for scale.
History
The square kilometre became the standard large-area unit with global metrication, replacing traditional units like the square league. It is the preferred unit for geographic and political area comparisons in international statistics and the United Nations system.
Common mistakes
Thinking 1 km² = 1,000 m². It is actually 1,000,000 m² (1 km × 1 km). Also, confusing square kilometres with kilometres squared in conversation, though mathematically they mean the same thing.
When is this conversion used?
Converting between acre and square kilometre is common when working across metric and imperial systems, such as international trade, travel between countries with different measurement standards, or following instructions from a different region.
Worked examples
1 acre = 0.00404686 square kilometre
1 square kilometre = 1,000,000 square metre
How to convert acre to square kilometre
To convert acre to square kilometre, multiply the value by 0.00404686.
To convert square kilometre back to acre, multiply by 247.10538147.
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 kilometre
| acre | square kilometre |
|---|---|
| 0.1 | 0.00040469 |
| 0.5 | 0.00202343 |
| 1 | 0.00404686 |
| 2 | 0.00809371 |
| 5 | 0.02023428 |
| 10 | 0.04046856 |
| 25 | 0.10117141 |
| 50 | 0.20234282 |
| 100 | 0.40468564 |
| 250 | 1.01171411 |
| 500 | 2.02342821 |
| 1,000 | 4.04685642 |
Common values
| acre | square kilometre | |
|---|---|---|
| A4 paper | 0.00001532 acre | 6.200000e-08 square kilometre |
| Parking space | 0.00308882 acre | 0.0000125 square kilometre |
| Tennis court | 0.06446238 acre | 0.00026087 square kilometre |
| Football field (soccer) | 1.76433242 acre | 0.00714 square kilometre |
| Central Park, NYC | 842.6293508 acre | 3.41 square kilometre |