Wavelength & Frequency Calculator
Convert between the wavelength and frequency of light and find the photon energy in joules and electronvolts.
How it works
c = λ × f · f = c / λ · λ = c / f · E = h × f · c = 299,792,458 m/s · h = 6.626×10⁻³⁴ J·s
Light travels at a fixed speed c, so its wavelength and frequency are inversely linked: a shorter wavelength means a higher frequency. Enter one and the calculator finds the other, then uses E = h·f to give the energy of a single photon in both joules and electronvolts (1 eV = 1.602×10⁻¹⁹ J).
Worked example
Green light of wavelength 500 nm has f = c ÷ (500×10⁻⁹) ≈ 599 THz and a photon energy of about 2.48 eV.
Frequently asked questions
Why is frequency shown in terahertz?
Visible-light frequencies are hundreds of trillions of hertz. Terahertz (10¹² Hz) keeps the numbers readable instead of writing out fourteen digits.
What is an electronvolt?
It is a tiny energy unit equal to 1.602×10⁻¹⁹ joules, convenient for single photons and atomic-scale physics. Visible photons carry a few electronvolts.
Does this apply to all light?
Yes. The relationship holds across the whole electromagnetic spectrum, from radio waves to gamma rays, as long as the wave travels in a vacuum at speed c.
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Educational estimate. Check the formula and units for your exact case.