How to calculate wave length
The "wavespeed" is the speed of light, which is 299,792,458 m/s if in free-space, or slowed by the root of the relative permittivity (dielectric constant for the material where the wave is propagating).  So $v = c/\sqrt{\epsilon_r}$ and the formula for wavelength is $\lambda = c/(f\sqrt{\epsilon_r})$, where $c$ is the speed of light (299,792,458 m/s), $f$ is the frequency of the signal in Hz, and $\epsilon_r$ is the dielectric constant.

Example dielectric constants:


Air at 0°C: 1.000594
Air at 20°C: 1.000528
Glass: 5 to 10
Paper: 3.85
Silicon: 11.68


For example, a 30 GHz signal in air would have a wavelength of nearly 10 mm: $ 299,792,458/30\times10^{9}$.