Convert $1 {\mathrm{mm}}^2 \mathrm{in} {\mathrm{cm}}^2$

 $1 {\mathrm{mm}}^2 = {(1 \mathrm{mm})}^2$  (We know that $\text{1mm=}\frac{1}{10}\mathrm{cm}$)

$={(\frac{1}{10} \mathrm{cm})}^2=\frac{1}{10} \mathrm{cm}\times \frac{1}{10} \mathrm{cm}$

$=\frac{1}{100} {\mathrm{cm}}^2$

Therefore, $1 {\mathrm{mm}}^2 = \frac{1}{100} {\mathrm{cm}}^2$.