Formula Wave in Vacuum Phase velocity Frequency Wavelength
$$v_{\text p} ~=~ \lambda \, f$$ $$v_{\text p} ~=~ \lambda \, f$$ $$f ~=~ \frac{ v_{\text p} }{ \lambda }$$ $$\lambda ~=~ \frac{ v_{\text p} }{ f }$$
Phase velocity
$$ v_{\text p} $$ Unit $$ \frac{\mathrm m}{\mathrm s} $$ Phase velocity is the speed of propagation of the same phase of a (monochromatic) wave.
In the case of electromagnetic waves, the phase velocity is the speed of light: \( c = \lambda \, f \), with the value \( c = 299 \, 792 \, 458 \, \frac{\mathrm m}{\mathrm s} \).
Frequency
$$ f $$ Unit $$ \mathrm{Hz} $$ Frequency of the wave. Indicates how often the wave (e.g. light wave) oscillates per second.
Wavelength
$$ \lambda $$ Unit $$ \mathrm{m} $$ Wavelength is the smallest distance between two points of the same phase. For example, the distance between two wave crests.