Convert Acre to Square Kilometer
Convert acres to square kilometers instantly. 1 acre = 0.0040468564 square kilometer — use the live calculator, the exact formula, a conversion table and worked examples. Also check the Square Kilometer to Acre converter for the reverse conversion.
Units explained
Acre
An acre is an imperial unit of area equal to exactly 4046.8564224 m². It is the most widely used non-metric unit for land area, particularly in the US, UK, and India.
Originally defined in medieval England as the area one yoke of oxen could plow in a day, approximately 40 perches by 4 perches. Standardized via the 1959 International Yard and Pound Agreement.
Acres are the standard land measurement unit in the US (real estate, agriculture), the UK (rural property), and widely used in India (alongside hectares and traditional regional units). 1 acre = 4840 sq yd = 43,560 sq ft = 0.4047 hectare.
Medieval English farming origin; modern exact value standardized in 1959.
Square Kilometer
A square kilometer is a metric unit of area equal to 1,000,000 m² (one million square meters), or 100 hectares. It is used for measuring large land areas, regional geography, and country-scale statistics.
Derived by squaring the kilometer (1000 m). The kilo- prefix comes from the Greek 'chilioi' (thousand).
Square kilometers express the area of cities, districts, lakes, forests, and entire countries. India's total area is approximately 3,287,263 km². 1 km² equals 100 hectares or about 247.105 acres.
Kilometer has been part of the metric system since 1795.
Acre to Square Kilometer conversion formula
The relationship between acres and square kilometers:
To convert acres to square kilometers, multiply the value in acres by 0.0040468564. To reverse, multiply square kilometers by 247.1053814672.
How to use this converter
Type a value into the calculator. The result in square kilometers updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Square Kilometer to Acre converter for the reverse direction.
Step-by-step: convert acres to square kilometers
- Write down the value in acres (ac).
- Multiply that value by the factor 0.0040468564.
- The product is the equivalent value in square kilometers (km²).
- To reverse, multiply the square kilometer value by 247.1053814672.
Worked examples
Example 1 — Convert 1 ac to km²:
1 × 0.0040468564 = 0.0040468564 km²
Example 2 — Convert 100 ac to km²:
100 × 0.0040468564 = 0.4046856422 km²
Real-world example — Coastal cruise distances
A 10-acre coastal sailing route converts to a different value in square kilometers — useful for cruise operators who switch between maritime, aviation, and road-distance units depending on the leg of the trip.
10 ac × 0.0040468564 = 0.0404685642 km²
Real-world example — Road-sign distances across systems
A 100-acre road sign converts cleanly into square kilometers — exactly the conversion drivers planning trips abroad rely on when reading road signs in a different measurement system.
100 ac × 0.0040468564 = 0.4046856422 km²
Real-world example — Endurance race distances
A 50-acre cycling or running race converts to a recognizable distance in square kilometers. Endurance athletes coming from a different measurement system use this conversion to compare training plans across regions.
50 ac × 0.0040468564 = 0.2023428211 km²
Acre to Square Kilometer conversion table
Standard reference values for converting acres to square kilometers:
| Acre [ac] | Square Kilometer [km²] |
|---|---|
| 0.01 | 4.046856e-5 |
| 0.1 | 0.0004046856 |
| 1 | 0.0040468564 |
| 2 | 0.0080937128 |
| 3 | 0.0121405693 |
| 4 | 0.0161874257 |
| 5 | 0.0202342821 |
| 10 | 0.0404685642 |
| 20 | 0.0809371284 |
| 30 | 0.1214056927 |
| 40 | 0.1618742569 |
| 50 | 0.2023428211 |
| 100 | 0.4046856422 |
| 500 | 2.0234282112 |
| 1000 | 4.0468564224 |
Frequently asked questions
How many square kilometers is 1 acre?
How do I convert acres to square kilometers?
How do I convert square kilometers back to acres?
How many square kilometers is 100 acres?
Popular area unit conversions
Convert Acre to other area units
Show all Acre conversions
Metric / SI (16 units)
Imperial / US Customary (14 units)
US Survey (5 units)
Indian Subcontinent (16 units)
Other Regional (10 units)
Scientific / Physics (5 units)
Historical / Pre-metric European (6 units)
Sources & references
Conversion factor (1 ac = 0.0040468564 km²) verified against the following authoritative sources:
- BIPM — The International System of Units (SI Brochure 9th ed.)
Official BIPM publication defining the seven SI base units (including the meter) and the rules for their use. The global authority on units of measurement.
- NIST — Guide to the SI
US National Institute of Standards and Technology reference covering the SI base and derived units with definitions and usage rules for US technical practice.
- NIST Special Publication 811 — Guide for the Use of the International System of Units
Detailed NIST guide covering exact conversion factors between SI and US customary units along with formatting and rounding conventions.
- NIST — Refinement of values for the yard and pound (Federal Register 1959)
The treaty (signed by US
- International Astronomical Union — System of Astronomical Constants
The IAU defines astronomical units including the AU (149597870700 m exactly) light-year and parsec used in astronomy and astrophysics.