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The square meter is the SI-derived unit of area. It has a symbol m² (33A1 in Unicode^[1]). It is defined as the area of a square whose sides measure exactly one meter. The square meter is derived from the SI base unit of the meter, which in turn is defined as the length of the path travelled by light in absolute vacuum during a time interval of ${\frac {1}{299792458}}$ of a second.

Adding SI prefixes creates multiples and submultiples. However, as the unit is squared, the order of magnitude difference between units doubles from their comparable linear units. For example, a kilometer is one thousand times the length of a meter, but a square kilometer is one million times the area of a square meter.

A "square meter" is not the same thing as a "meter square" ^[source?] - although it is true that exactly 1 square meter is exactly 1 meter square. But that only works for the number 1; no other.

For example, a square that is 2 meters long and 2 meters wide has 4 square meters of area.

$2m*2m=4m^{2}$

But a square that is 4 meters squared would have 4 meters on each side. This means it would have 16 square meters of area.

$4m*4m=16m^{2}$

That is, $(4m)^{2}$ is 4 meters squared, whereas $4m^{2}$ is 4 square meters.

SI prefixes applied to the square meter

The square meter may be used with all SI prefixes used with the meter.

Multiple	Name	Symbol	Multiple	Name	Symbol
10⁰	square meter (centiare)	m²	10⁰	square meter (centiare)	m²
10²	square decameter (are)	dam²	10⁻²	square decimeter	dm²
10⁴	square hectometer (hectare)	hm²	10⁻⁴	square centimeter	cm²
10⁶	square kilometer	km²	10⁻⁶	square millimeter	mm²
10¹²	square megameter	Mm²	10⁻¹²	square micrometer	µm²
10¹⁸	square gigameter	Gm²	10⁻¹⁸	square nanometer	nm²
10²⁴	square terameter	Tm²	10⁻²⁴	square picometer	pm²
10³⁰	square petameter	Pm²	10⁻³⁰	square femtometer	fm²
10³⁶	square exameter	Em²	10⁻³⁶	square attometer	am²
10⁴²	square zettameter	Zm²	10⁻⁴²	square zeptometer	zm²
10⁴⁸	square yottameter	Ym²	10⁻⁴⁸	square yoctometer	ym²