ConverterHub

Wavelength Calculator

Find wavelength from frequency.

How it is calculated

For any wave travelling at the speed of light, wavelength and frequency are linked by λ = c ÷ f. Here λ is the wavelength in metres, f is the frequency in hertz (cycles per second) and c is the speed of light in a vacuum, fixed in the tool at 299,792,458 m/s. Enter the frequency in plain hertz, so 100 MHz is 100000000. The frequency must be above zero, and the answer is rounded to two decimals in metres. This applies to radio, light and other electromagnetic waves. Sound and water waves travel at much lower speeds, and light in glass or cable is slower than in a vacuum, so the result would not apply to them.

Worked example

An FM radio station broadcasts at 100 MHz, which is 100,000,000 Hz. Divide the speed of light by this frequency: 299,792,458 ÷ 100,000,000 = 2.99792458. Rounded to two decimals the tool shows 3.00 m. This is why FM antennas are often sized in fractions of a metre, such as a half-wave dipole of about 1.5 m.

Try this example →

Common mistakes

  • Entering 100 for 100 MHz. The field is in hertz, so you must type 100000000 or the answer will be about 3 million metres.
  • Using this for sound. Sound travels at roughly 343 m/s in air, not at the speed of light, so the result would be wrong by a factor of nearly a million.
  • Forgetting that wavelength gets shorter as frequency rises. Doubling the frequency halves the wavelength.
  • Confusing the result with antenna length. A practical antenna is a fraction of the wavelength, often a half or quarter.
  • Reading the rounded 3.00 m as exact when you need precision at high frequencies, where the extra decimals matter.

About this calculator

This calculator applies the wave equation λ = v/f (wavelength equals wave speed divided by frequency) to find a wave's physical length from its frequency, using the speed of light (≈3×10⁸ m/s) for electromagnetic waves like radio and light, or the speed of sound (≈343 m/s in air) for acoustic waves. Higher frequency always produces a shorter wavelength, and the calculator handles the very different scales involved — radio wavelengths in metres versus visible light in nanometres.

Radio and antenna engineers sizing an antenna to a specific frequency (an antenna is typically a fraction of its target wavelength), audio engineers working out room acoustics or speaker placement, and physics students converting between the frequency and wavelength of light all rely on this same relationship.

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