Enter a photon's wavelength (in nm, μm, or m) and this Wavelength to Energy Calculator returns its energy in joules (J) and electronvolts (eV), plus the corresponding frequency. Based on Planck's equation (E = hc/λ), results update the moment you change the wavelength or unit selection.
Photon Energy (eV)
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Photon Energy (J)
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Frequency (Hz)
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Wavenumber (cm⁻¹)
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Use Planck's equation: E = hc/λ, where h is Planck's constant (6.626 × 10⁻³⁴ J·s), c is the speed of light (2.998 × 10⁸ m/s), and λ is the wavelength in metres. Divide hc by the wavelength to get the energy in joules. To convert to electronvolts, divide by 1.602 × 10⁻¹⁹.
Convert your wavelength to metres first (e.g. 1 nm = 1 × 10⁻⁹ m). Then apply E = (6.626 × 10⁻³⁴ × 2.998 × 10⁸) / λ. For a 500 nm photon, E ≈ 3.976 × 10⁻¹⁹ J. This calculator handles the unit conversion and arithmetic automatically.
First calculate energy in joules using E = hc/λ, then divide by the elementary charge e = 1.602 × 10⁻¹⁹ C to get electronvolts. A useful shortcut is E (eV) ≈ 1240 / λ (nm), which gives a quick estimate for wavelengths in the visible spectrum.
A 100 nm photon (ultraviolet range) has an energy of approximately 12.40 eV or 1.99 × 10⁻¹⁸ J. This is energetic enough to ionise many atoms, which is why UV radiation at these wavelengths is used in photolithography and can cause DNA damage.
Convert 3.5 μm to metres: 3.5 × 10⁻⁶ m. Then E = (6.626 × 10⁻³⁴ × 2.998 × 10⁸) / (3.5 × 10⁻⁶) ≈ 5.68 × 10⁻²⁰ J, or about 0.354 eV. This falls in the mid-infrared region, commonly used in thermal imaging and spectroscopy.
Wavelength and photon energy are inversely proportional — shorter wavelengths correspond to higher energy photons, and longer wavelengths to lower energy. This is expressed by E = hc/λ. For example, blue light (~450 nm) carries more energy per photon than red light (~700 nm).
Planck's constant (h = 6.626 × 10⁻³⁴ J·s) is a fundamental physical constant that quantifies the relationship between a photon's energy and its frequency. It was introduced by Max Planck in 1900 and forms the cornerstone of quantum mechanics, showing that energy is exchanged in discrete packets called quanta.
Frequency and wavelength are related by f = c / λ, where c is the speed of light (~3 × 10⁸ m/s). As wavelength increases, frequency decreases, and vice versa. Since E = hf, higher frequency (shorter wavelength) means higher energy. This calculator shows both the frequency and energy for your input wavelength.