Wavelength & Frequency Calculator
With the photon energy that makes the spectrum mean something.
Work out Wavelength & Frequency. With the photon energy that makes the spectrum mean something. Shows the working, not just the answer.
Frequency
5.9958 × 10^14 Hz
Green light
Speed equals wavelength times frequency, for any wave at all. Fix the speed and the two become reciprocal — double the frequency and the wavelength halves, which is why the electromagnetic spectrum can be labelled equally well by either. Photon energy is what makes the spectrum meaningful. The difference between a radio wave and a gamma ray is entirely the energy each photon carries, and around 3 eV — the ultraviolet boundary — is where photons start having enough energy to break chemical bonds. That threshold is what "ionising radiation" means. Wave speed depends on the medium, and it is the speed that changes rather than the frequency. Light entering water slows to about three quarters of its vacuum speed, so its wavelength shortens by the same factor while its frequency — and therefore its colour — is unchanged.
How the Wavelength & Frequency Calculator works
Convert between wavelength and frequency for light or sound, with the photon energy and the spectral region. Photon energy is what decides whether radiation is ionising, which is the only reason the spectrum's divisions matter.
Also known as: convert nm to thz · photon energy from wavelength · what frequency is green light · wavelength of a 440 hz sound
Frequently asked questions
How do you convert wavelength to frequency?
Divide the wave speed by the wavelength. For light in vacuum that is 299,792,458 m/s, so 500 nm gives about 600 THz.
What is photon energy?
Planck's constant times frequency. It is what separates a harmless radio wave from an ionising gamma ray — same phenomenon, energies differing by a factor of a trillion.
Where does ionising radiation begin?
Around 3 to 10 eV, in the ultraviolet, where photons carry enough energy to break chemical bonds and knock electrons off atoms. Below that, radiation can heat things but cannot damage DNA directly.
Does light change colour underwater?
No. Entering water slows light and shortens its wavelength by about a quarter, but the frequency is unchanged — and frequency is what the eye responds to, so the colour stays the same.
Does this work for sound?
Yes, with the right speed. Sound in air at 20 °C travels at 343 m/s, so a 440 Hz A has a wavelength of 78 cm. The photon energy and spectral band do not apply, and the calculator says so.
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