What is square kilometers?

The square meters is a unit used to measure area. It is part of SI unit system and has the symbol m^2 ($m^2$)

$$1\ km^2 = 1×10^{6} m^2 = 1×10^12\ mm^2$$

$$1\ km^2 = 1.0763911×10^7 ft^2 = 1.195990×10^6 yd^2 = 1.550031×10^9 in^2$$

Wikipedia page for Square kilometre

What is square millimeters?

The square millimeters is a unit used to measure area. It is part of SI unit system and has the symbol mm^2 ($mm^2$)

$$mm^2 = 10^{-6} m^2 = 10^{-12} km^2 = 10.763911*10^{-6} ft^2 = 1.195990 *10^{-6} yd^2 = 1550.0031*10^{-6} in^2$$

Wikipedia page for Square metre