How many square kilometers are in 1 acre?

1 acre equals 0.0040468564 square kilometers, using the exact defined conversion factor rather than an estimate.

How do I convert acre to square kilometer?

Multiply the acre value by 0.004046856422. The converter above does this instantly to whatever precision you set.

How do I convert square kilometer back to acre?

Use the reverse factor: 1 square kilometer equals 247.1053815 acres. You can also use the swap control in the converter above to flip the direction instantly.

Is the acre to square kilometer conversion exact?

Yes. The international acre is defined as exactly 4,046.8564224 square meters. That fixed definition is what the converter above uses, so any rounding you see is a display choice, not a limitation of the math.

Acres to Square Kilometers Converter

Q: What is a acre?

Acre (ac) measures area. The international acre is defined as exactly 4,046.8564224 square meters. It is classified as a US/imperial customary unit.

Q: What is a square kilometer?

Square Kilometer (km2) measures area. A square kilometer is one million square meters — the area of a 1 km × 1 km square. It is classified as a SI derived (metric prefix) unit.

About Converting Acres to Square Kilometers

Acre and Square Kilometer both measure a farming-related quantity — a land area or an application/yield rate per unit area — used to report crop yields, calculate how much fertilizer or seed a field needs, and plan irrigation. Acre is typically associated with united States, while Square Kilometer is typically associated with used worldwide for city, region, and country-scale area reporting..

Formula

square kilometers = acres × 0.0040468564224

This factor comes from each unit's defined relationship to the category's base unit: 1 acre equals 4046.8564224 base units, and 1 square kilometer equals 1000000 base units, so dividing one by the other gives the direct acre-to-square kilometer factor of 0.0040468564224.

Simple example

1 ac × 0.004046856422 = 0.0040468564 km2

1 acre = 0.0040468564 square kilometers.

Real-world example

100 ac × 0.004046856422 = 0.4046856422 km2

100 acres = 0.4046856422 square kilometers.

Conversion table

Acre (ac)	Square Kilometer (km2)
1 ac	0.0040468564 km2
5 ac	0.0202342821 km2
10 ac	0.0404685642 km2
50 ac	0.2023428211 km2
100 ac	0.4046856422 km2
500 ac	2.023428211 km2

Reverse conversion: Square Kilometer to Acre

0.0040468564 km2 × 247.1053815 = 0.9999999945 ac

0.0040468564 square kilometers = 0.9999999945 acres.

acres = square kilometers × 247.105381467

For a page dedicated to this direction, see Square Kilometer to Acre.

Acre vs. Square Kilometer

Aspect	Acre	Square Kilometer
Family	US/imperial customary unit	SI derived (metric prefix) unit
Typical use	Measuring farmland, ranch, and rural property size in the US	National and regional land-area statistics
Where it's used	United States	Used worldwide for city, region, and country-scale area reporting.

Understanding the Acre

Acre (ac) measures area. The international acre is defined as exactly 4,046.8564224 square meters. It is classified as a US/imperial customary unit.

Where it's used: United States United Kingdom (informal/historical, land registry legacy) Countries with historical British land-survey systems

International acre vs. US survey acre. The US survey acre, based on the US survey foot, differs from the international acre by about two parts per million. The US retired the survey foot/acre for federal use at the end of 2022.

Uses of the Acre today

Measuring farmland, ranch, and rural property size in the US
Real estate listings and zoning for land parcels
Forestry and land-management reporting

History of the Acre

The acre originated in medieval England as a practical field measurement: the area a yoke of oxen could plow in one day, roughly a furlong (660 ft) long by a chain (66 ft) wide, giving the 43,560 square feet still used today.

Edward I's 1305 statute formalized this figure. In 1959, the same International Yard and Pound Agreement that fixed the pound also fixed the international acre at exactly 4,046.8564224 m², though the US separately retained a slightly different 'US survey acre' for some legacy land records until it was phased out in 2023.

Historical origin. Acre was not the invention of a single named person; it developed through the process described above.

Understanding the Square Kilometer

Square Kilometer (km2) measures area. A square kilometer is one million square meters — the area of a 1 km × 1 km square. It is classified as a SI derived (metric prefix) unit.

Where it's used: Used worldwide for city, region, and country-scale area reporting.

Uses of the Square Kilometer today

National and regional land-area statistics
City and urban planning at large scale
Geography and cartography

History of the Square Kilometer

Like other metric-prefixed area units, the square kilometer follows automatically from the kilometer once the meter was standardized in the 1790s French metric reform.

Historical origin. Square Kilometer was not the invention of a single named person; it developed through the process described above.

Acre — sources

NIST — US Survey Foot: Revised Unit Conversion Factors — Documents the 1959 international acre definition and the 2022/2023 survey-foot retirement.

Square Kilometer — sources

BIPM SI Brochure — Coherent derived units — Basis for metric-prefixed area units.

Acres to Square Kilometers Converter — ac to km2

Agriculture Converter