The wavelength of a wave is related to its frequency and the speed of the wave by the expression. Wavelength and frequency of a wave are related by the equation Velocity Wavelength x Frequency where the velocity is the speed of a wave peak as it passes a stationary point. As the energy transported by an electromagnetic wave increases so does its frequency whilst its wavelength gets shorter.
You can measure wavelength from peak to peak or from trough to trough.
The frequency of a wave is the number of waves produced by a source each second. We know the relationship between wavelength represented by l and frequency represented by n according to to which they are inversely related and their product is the velocity of wave and in case of photon it is represented by c. The relationship between wavelength and frequency is that the frequency of a wave multiplied by its wavelength gives the speed of the wave as we will see below. You can measure wavelength from peak to peak or from trough to trough.