A square mile (mi2) is a unit of measurement of area. 1 square mile is equal to the area of a square with sides that measure 1 mile:
A square area is a measurement made up of two lengths. Square units of area, such as square miles, are a result of multiplying two lengths. In the case of square miles, each length is measured in miles, so multiplying miles × miles results in miles2. The measured area does not need to be in the shape of a square; any area can be calculated, or estimated, as the area made up by some number of unit squares.
For example, a 4 mi × 2 mi rectangle is made up of 8 squares with an area of 1 mi2 each. The rectangle therefore has an area of 8 mi2:
Systems of measurement
In the US customary system of units, square inches, square feet, square yards, square miles, and acres are some of the primary measurements of area. Square inches, feet, and yards are used for small to medium measurements of area, while square miles and acres are used for larger areas. For example, the area of Yosemite National Park may be reported using square miles (1169.432 mi2) or acres (748,436 acres).
The standard unit of area in the International System of Units (SI) is the square meter (or metre). SI makes use of prefixes that denote the specific power of 10 that modifies a base unit (in this case the meter). For example the "kilo-" prefix indicates 103, so 1,000 meters is equal to 1 kilometer, making 1,000,000 m2 = 1 km2. Converting between SI units is relatively straightforward because units are related by powers of 10.
Outside of the US, certain US customary units such as square feet may still be used, but for the most part, area is measured in square meters. As such, it is important to be able to convert between US customary and SI units of area since most countries around the world use SI, US customary units, or a mixture of SI and imperial (similar to US customary system) units of measurement.
Below are the relationships between square miles and some other measurements of area.
1 square mile = 27,878,400 square feet
1 square mile = 640 acres
1 square mile = 2,589,988.110 square meters
Note that these conversions are rounded to 3 decimal places, so they are not exact.
Convert the following areas between square miles, acres, and square kilometers.
1. 349 mi2:
349 × 2.59 = 903.91 km2
349 × 640 = 223,360 acres
2. 1111 km2:
1111 ÷ 2.59 = 428.958 mi2
1111 × 247.105 = 274,533.655 acres