A square mile (mi²) is a unit of area equal to the area of a square with sides measuring one mile. It is a customary unit, primarily used in the United States and the United Kingdom. One square mile is defined as 2.58999 square kilometers.
The square mile has roots in the English system of measurement. It became defined in the 18th century as land measurement expanded. The mile itself has ancient origins, initially based on Roman measurements. The square mile gained prominence as land surveying and property measurement became standardized.
Square miles are commonly used in land measurement, particularly in real estate, agriculture, and urban planning. It is often applied in geographical studies, such as measuring the area of states or countries. The unit is significant in the context of population density calculations.