Photon Energy Calculator

The Photon Energy Calculator works out the energy carried by a single photon of light from either its wavelength or its frequency, using the famous relation E = hf = hc/λ. It returns the energy in both joules and electronvolts (eV), gives you the matching frequency and wavelength, shows the energy per mole of photons for chemistry, and places the photon on a visual electromagnetic spectrum — even revealing its true color when it falls in the visible range.

What Is Photon Energy?

Light is made of tiny packets of energy called photons. Each photon carries a fixed amount of energy that depends only on its frequency (or equivalently its wavelength) — not on how bright the light is. A brighter beam simply contains more photons; each individual photon still carries the same energy. This quantization of light energy, introduced by Max Planck and Albert Einstein, is a cornerstone of quantum physics and explains phenomena like the photoelectric effect.

Photon Energy Formula

There are two equivalent ways to write the photon energy equation, linked by the wave relation c = fλ:

where:

• E — photon energy (joules, J)
• h — Planck's constant = 6.62607015 × 10⁻³⁴ J·s
• f — frequency (hertz, Hz)
• c — speed of light = 2.99792458 × 10⁸ m/s
• λ — wavelength (metres, m)

To express the answer in electronvolts, divide the energy in joules by 1.602176634 × 10⁻¹⁹ J/eV. A handy shortcut worth remembering is E (eV) ≈ 1240 / λ (nm), which comes straight from hc expressed in eV·nm.

The Electromagnetic Spectrum

Photon energy rises as wavelength shrinks. The table below shows the main bands from lowest energy (radio) to highest (gamma rays):

Photon Energy of Common Light Sources

Why Photon Energy Matters

How to Use This Calculator

1. Choose what you know: pick Wavelength, Frequency, or Energy from the first dropdown.
2. Enter the value and unit: type your number and select the matching unit (nm, µm, GHz, THz, eV, and more).
3. Click Calculate: the tool applies E = hf = hc/λ and converts to every unit at once.
4. Review your results: read the energy in joules and eV, the energy per mole, the spectrum position, and the visible color if the photon is in the visible range.

Frequently Asked Questions

What is the formula for photon energy?

Photon energy is E = hf, where h is Planck's constant (6.62607015 × 10⁻³⁴ J·s) and f is the frequency. Because the speed of light c equals frequency times wavelength, this is equivalent to E = hc / λ, so you can compute energy directly from wavelength as well.

How do I convert photon energy from joules to electronvolts?

Divide the energy in joules by 1.602176634 × 10⁻¹⁹, the number of joules in one electronvolt. For example, a 3.06 × 10⁻¹⁹ J photon has an energy of about 1.91 eV, which is a typical red light photon.

What is the energy of a photon of visible light?

Visible light spans roughly 380 nm (violet) to 750 nm (red). Violet photons carry about 3.3 eV, green about 2.4 eV, and red about 1.7 eV. In joules these are on the order of 3 to 5 × 10⁻¹⁹ J per photon.

Does a shorter wavelength mean more energy?

Yes. Photon energy is inversely proportional to wavelength (E = hc / λ), so shorter wavelengths carry more energy. Gamma rays and X-rays have very short wavelengths and very high energy, while radio waves have long wavelengths and very low energy.

What is the energy per mole of photons?

Multiply the single-photon energy in joules by Avogadro's number (6.022 × 10²³) to get the energy of one mole of photons, often called an einstein. Dividing by 1000 gives kilojoules per mole, which is convenient for photochemistry. Red light at 650 nm is about 184 kJ/mol.

When does a photon become ionizing radiation?

Photons with energy above roughly 10 eV can strip electrons from atoms and are considered ionizing. This includes far ultraviolet, X-rays, and gamma rays. Visible light, infrared, microwaves, and radio waves are non-ionizing because their energy is far below this threshold.

Additional Resources

• Photon Energy - Wikipedia
• Planck Constant - Wikipedia
• Electromagnetic Spectrum - Wikipedia