Convert wavelength and frequency. This free calculator uses c = f × λ for electromagnetic waves, solving either from the other, and shows the photon energy and where it sits on the spectrum.
Solve for
For electromagnetic waves (light, radio, etc.) in a vacuum, c = f × λ. Enter the one you know and pick its unit; the other is found from the speed of light.
Frequency
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Enter a value
Wavelength
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Frequency
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Photon energy
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EM band
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Uses the speed of light c = 299,792,458 m/s. Photon energy is E = h × f (h = Planck’s constant). For sound or other waves, the wave speed differs from c, so use the relevant speed instead.
Use this free wavelength frequency calculator to convert between the wavelength and frequency of electromagnetic waves using c = f × λ. It also gives the photon energy and the part of the spectrum.
What this wavelength frequency calculator does
This wavelength frequency calculator links the frequency and wavelength of light, radio and other electromagnetic waves. Enter one and it finds the other from the speed of light, plus the photon energy and the spectrum band.
The wave equation
c = f × λ
f = c / λ λ = c / f
photon energy: E = h × f
(c = 299,792,458 m/s, h = Planck's constant)
So green light at 500 nm has a frequency of about 600 THz and a photon energy near 2.48 eV; a 100 MHz FM signal has a 3 m wavelength.
The electromagnetic spectrum
Band
Frequency
Wavelength
Radio
< 3 GHz
> 10 cm
Microwave
3–300 GHz
1 mm – 10 cm
Infrared
0.3–400 THz
700 nm – 1 mm
Visible
~400–790 THz
380–700 nm
Ultraviolet
790 THz – 30 PHz
10–380 nm
X-ray / gamma
> 30 PHz
< 10 nm
Wavelength and frequency are inversely related
Higher frequency means shorter wavelength, and vice versa — their product is always the speed of light. Higher-frequency waves also carry more energy per photon.
How to use the wavelength frequency calculator
Choose frequency or wavelength to solve for.
Enter the known value and pick its unit.
Read the result, photon energy and spectrum band.
Wavelength & Frequency FAQ
How do I convert wavelength to frequency?
Divide the speed of light by the wavelength: f = c / λ. For example, 500 nm gives about 6 × 10¹⁴ Hz (600 THz).
How do I convert frequency to wavelength?
Divide the speed of light by the frequency: λ = c / f. A 100 MHz signal has a wavelength of about 3 metres.
What is the formula linking them?
c = f × λ, where c is the speed of light (299,792,458 m/s). Frequency and wavelength are inversely related.
How is photon energy calculated?
With E = h × f, where h is Planck’s constant. Higher-frequency light carries more energy per photon — 500 nm light is about 2.48 eV.
Does this work for sound waves?
The formula is the same shape, but sound travels at the speed of sound, not light. Use the speed of sound for acoustic wavelengths.
Is the wavelength frequency calculator free?
Yes, this wavelength frequency calculator is completely free, needs no sign-up, and gives instant results in your browser.
