# Square kilometers

A square kilometer (km^{2}) is a unit of measurement of area. 1 square kilometer is equal to the area of a square with sides that measure 1 kilometer.

A square area is a measurement made up of two lengths. Square units of area, such as square kilometers, are a result of multiplying two lengths. In the case of square kilometers, each length is measured in kilometers, so multiplying kilometers × kilometers results in km^{2}. 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 km × 2 km rectangle is made up of 8 squares with an area of 1 km^{2} each. The rectangle therefore has an area of 8 km^{2}:

## Systems of measurement

A square kilometer is a unit of area in the International System of Units (SI), the most widely used system of measurement. Square kilometers are derived from square meters, the SI base unit of area. SI makes it relatively easy to convert an SI unit of area, such as square meters, into larger or smaller measurements of area. This is because SI makes use of prefixes that indicate a specific power of 10 by which the base unit, in this case the meter, is modified. For example, the "kilo-" prefix indicates 10^{3}, so to express an area such as 10 m^{2} in km^{2} multiply by (10^{3})^{2}, or 1,000,000. This is because there are 1,000 meters in a kilometer, and (1,000 m)^{2} (since we are talking about area not length) is 1,000,000 m^{2}.

It can also be useful to know how to convert between different measurements of area, particularly for those who live in the US, since the US primarily uses US customary units of measurement. Below are the relationships between square kilometers, square meters, and some US customary measurements of area.

1 square kilometer = 1,000,000 square meters

1 square kilometer = 10,763,910.417 square feet

1 square kilometer = 247.105 acres

2.59 square kilometers = 1 square mile

Note that these conversions are rounded to 3 decimal places, so they are not exact.

Examples

Convert the following areas between square kilometers, square miles, and acres.

1. 27 km^{2}:

27 ÷ 2.59 = 10.425 mi^{2}

27 × 247.105 = 6671.835 acres

2. 649 mi^{2}:

649 × 2.59 = 1680.91 km^{2}

649 × 640 = 415,360 acres

3. 2,458,346 acres:

2,458,346 ÷ 247.105 = 9,948.589 km^{2}

2,458,346 ÷ 640 = 3841.166 mi^{2}