One acre equals exactly 43,560 square feet, or about 4,047 square meters. An acre was historically the amount of land a yoke of oxen could plow in one day. One hectare equals 2.471 acres, and there are 640 acres in one square mile.

A hectare is a metric unit equal to 10,000 square meters (100 m × 100 m), while an acre is an imperial unit equal to 4,047 square meters. Hectares are used in most countries for agricultural and land measurement; acres remain common in the United States and United Kingdom.

Multiply square meters by 10.7639 to get square feet. For example, a 50 m² apartment equals approximately 538 square feet. To reverse, divide square feet by 10.7639 (or multiply by 0.0929).

One square kilometer equals 0.386 square miles, so 1 square mile equals about 2.59 square kilometers. Urban areas are often measured in square kilometers in metric countries and square miles in the US. For reference, Manhattan island is about 59 square kilometers (23 square miles).

Real estate commonly uses square feet or square meters for interior space, and acres or hectares for land. Scientific and geographic contexts use square meters and square kilometers exclusively. Agriculture typically uses hectares internationally, with acres still common in the US and UK.