Use the formula: wavelength = speed ÷ frequency
For light in vacuum, use: wavelength = 3.00 × 10^8 m/s ÷ frequency
For waves on a string or sound waves, use: wavelength = wave speed ÷ frequency
Measure the wave speed if it is not already known
Measure the frequency in hertz
Divide the wave speed by the frequency
Use the result in meters
If needed, convert meters to nanometers, centimeters, or millimeters
For electromagnetic waves, use: wavelength = c ÷ frequency
For a wave graph, measure the distance between two identical points on consecutive waves
For a crest-to-crest or trough-to-trough measurement, use the horizontal distance between them
For a wave equation, identify the wavelength from the wave number using: wavelength = 2π ÷ wave number