Photon Energy Calculator

Photon energy is calculated using Planck's equation: E = hf, where h is Planck's constant (6.626 × 10⁻³⁴ J·s) and f is the photon's frequency. Equivalently, since c = fλ, you can write E = hc/λ, where λ is the wavelength and c is the speed of light (≈ 3 × 10⁸ m/s). Enter either the wavelength or frequency above to get the energy in joules and electronvolts.

A photon with a wavelength of 450 nm (blue-violet visible light) has an energy of approximately 4.42 × 10⁻¹⁹ J, or about 2.76 eV. You can verify this by entering 450 nm in the calculator above.

Gamma-ray photons are the most energetic in the electromagnetic spectrum, with energies exceeding 100 keV (100,000 eV). They have extremely short wavelengths (below 0.01 nm). X-rays and ultraviolet photons are the next most energetic, while radio wave photons have the lowest energies.

Both joules and electronvolts measure the same physical quantity — energy — but at very different scales. One electronvolt equals 1.602 × 10⁻¹⁹ joules. Because photon energies are extremely small, electronvolts are the more practical unit in atomic and optical physics. Joules are the SI standard unit and are used in engineering and broader physics contexts.

Radio waves have photon energies below ~10⁻⁶ eV. Microwaves range from ~10⁻⁶ to 10⁻³ eV. Infrared photons span ~0.001 to 1.7 eV. Visible light falls between ~1.7 eV (red, ~700 nm) and ~3.3 eV (violet, ~380 nm). Ultraviolet photons range from ~3 to 124 eV. X-rays cover ~100 eV to 100 keV, and gamma rays go above that.

Yes. Frequency and wavelength are related by c = fλ, so they contain the same information. Using E = hf is often more direct when you know the frequency. Simply switch the calculator input mode to 'Frequency', enter the value, and select the appropriate unit (Hz, GHz, THz, etc.).

Planck's constant (h) is a fundamental physical constant equal to 6.62607015 × 10⁻³⁴ J·s. It defines the relationship between a photon's energy and its frequency. It was introduced by Max Planck in 1900 to explain blackbody radiation and is a cornerstone of quantum mechanics.

From the equation E = hc/λ, energy is inversely proportional to wavelength. A shorter wavelength means higher frequency (since c = fλ), and higher frequency means more oscillations per second, which translates to greater energy per photon. This is why UV and X-ray photons are far more energetic — and potentially more damaging — than visible or infrared light.