Convert Acre to Square Kilometer

The acre has its origins in medieval England, where it was used as a unit of area for measuring land, particularly for agricultural purposes. The term "acre" comes from the Old English word "aecer", which referred to a field or a piece of land. The unit was historically defined as the area that could be plowed in one day by a team of oxen. The standard definition of an acre as 43,560 square feet was established in the 18th century, and it has been widely adopted in countries that use the imperial or U.S. customary systems. Despite the global adoption of the metric system, the acre remains a standard unit for land measurement in the United States and other regions that follow imperial units.

The square kilometer is derived from the kilometer, which is a unit of length in the metric system. The kilometer itself was introduced in the 18th century as part of the metric system, based on the meter, which was originally defined as one ten-millionth of the distance from the North Pole to the equator. The square kilometer, like other area units in the metric system, is based on the square of the unit of length. As the metric system became more widely adopted worldwide, the square kilometer became a standard unit for measuring large areas, particularly in geography, urban planning, and land management.