How to Calculate Wavelength With a Formula

FM radiowaves are about 3 feet long.

The wavelength is a measure between crests of adjacent waves or troughs of adjacent waves. While wavelength may sometimes be directly measured, often it is simpler to calculate the wavelength based on the frequency and speed of the wave. The speed of the wave is equal to the frequency multiplied by the wavelength (wave speed = frequency x wavelength), and this equation may be rewritten to allow wave speed and frequency to solve for wavelength. This is especially useful when measuring the wavelengths of electromagnetic waves since these waves travel at the speed of light which is a known value. This leaves determining the frequency as the only prerequisite to calculating the wavelength.

Things You'll Need

• Pencil
• Paper

Instructions

1. Measure the speed of the wave. For electromagnetic waves such as light and radio waves, the speed is the speed of light defined at 299,792,458 meters per second. For mechanical waves such as sound and ocean waves, the speed of the wave is much less and must be determined.

2. Divide the speed of the wave by the frequency to calculate the wavelength (wavelength = wave speed ÷ frequency). For example, a radiowave with a frequency of 90 MHz (MHz means megahertz with one megahertz equaling one million waves per second) has a wavelength of 3.33 m. This is determined by dividing the frequency (90,000,000 waves per second) by the speed which in this case is the speed of light (299,792,458 m per second) to yield 3.33 m (299,792,458 m per second ÷ 90,000,000 waves per second = 3.33 m).

3. Practice this equation on different speeds.

References

• University of California San Diego: Frequency
• NASA: Electromagnetic Spectrum