**The square metre ** is the SI derived unit of area, with symbol m^{2}. It is the area of a square whose sides measure exactly one metre. The square metre is derived from the SI base unit of the metre, which itself is defined as the length of the path travelled by light in absolute vacuum during a time interval of ^{1}/_{299,792,458} of a second.

**Square kilometre** symbol km^{2}, is a multiple of the square metre, the SI unit of area or surface area.
1 km^{2} is equal to:

- 1,000,000 square metres (m
^{2}) - 100 hectares (ha)

It is also approximately equal to:

- 0.3861 square miles
- 247.1 acres

Conversely:

- 1 m
^{2}= 0.000001 (10^{−6}) km^{2} - 1 hectare = 0.01 (10
^{−2}) km^{2} - 1 square mile = 2.5899km
^{2} - 1 acre = about 0.004047km
^{2}