The square mile (abbreviated as sq mi and sometimes as mi²) is an imperial and US unit of measure for an area equal to the area of a square with a side length of one statute mile. It should not be confused with miles square, which refers to a square region with each side having the specified length. For instance, 20 miles square (20 × 20 miles) has an area equal to 400 square miles; a rectangle of 10 × 40 miles likewise has an area of 400 square miles, but it is not 20 miles square.
One square mile is equal to:
Since one inch has been standardized to 2.54 cm by international agreement, a square mile is equivalent to the following metric measures:
When applied to a portion of the earth's surface, "square mile" is an informal synonym for section.
Romans derived measurements from marching. Five feet was equal to one pace (which is appropriately a double step). 1,000 paces measured a Roman mile, which was somewhat smaller than the English statute mile. This Roman system was adopted, with local variations, throughout Europe as the Roman Empire spread.
Total population in a square mile is derived by dividing the total number of residents by the number of square miles of land area in the specified geographic area. The population per square kilometer is derived by multiplying the population per square mile by 0.3861.
Land area measurements are originally recorded as whole square meters. Square meters are converted to square kilometers by dividing by 1,000,000; square kilometers are converted to square miles by dividing by 2.58999; square meters are converted to square miles by dividing by 2,589,988.