Acre (ac)
The acre, or ac, is a unit of area used in the imperial and US systems. It originated in medieval England and referred to the land a team of oxen could plow in a day. Today, one acre is 4,840 square yards or 4,046.856 square meters. Acres are still used in the US, Canada, and the UK for real estate, land sales, and farms. While the metric system is more common worldwide, the acre is still used because it is part of tradition and is easier to use in daily life.
Square Kilometer (km²)
The square kilometer, or km², is equal to one million square meters. It was designed for measuring large areas when the metric system was introduced. Square kilometers are often used in geography, maps, and environmental studies to represent the size of places such as cities, forests, and countries. For example, a country’s size is typically measured in square kilometers (km²). Its ease of use and simple conversions make it important for sharing global information.