So to calculate the wavelength from the frequency as you want to do we need to know the speed. The wavelength is calculated from the wave speed and frequency by l wave. Determine the waves frequency.
C Speed of Light 299792458 ms f Frequency.
For instance lets use the frequency of a radio waves spectrum which is f 10 MHz. Wave energy from graphs. C Speed of Light 299792458 ms f Frequency MHz. Calculating frequency and wavelength from displacement graphs.