Use the formula: frequency = wave speed ÷ wavelength
Write it as: f = v / λ
Measure the wave speed in meters per second
Measure the wavelength in meters
Divide the wave speed by the wavelength
The result is the frequency in hertz
Use the formula: frequency = 1 ÷ period
Write it as: f = 1 / T
Measure the period in seconds
Divide 1 by the period
The result is the frequency in hertz