Units of wave number are

$\left(\overline{\mathrm{\vartheta }}\right)$ it is reciprocal of $\mathrm{\lambda }$

$\overline{\mathrm{\vartheta }}$$=\frac{1}{\mathrm{\lambda }}$

𝜆  can be measured in Å , pm & nm.

These can be measured in cm & m

So reciprocal gives ${\mathrm{cm}}^{-1}$ & ${\mathrm{m}}^{-1}$.