Photon Energy Calculator - Wavelength or Frequency to eV

A photon energy calculator turns any wavelength or frequency of electromagnetic radiation into the energy carried by a single photon, using E = hν = hc/λ. Enter a wavelength in nanometres or a frequency in terahertz and the calculator returns the photon energy in joules and electronvolts, the implied frequency and wavelength, the photon momentum, the wave number, and the photon flux for the entered beam power.

• • Coursework checks: Verify homework answers for a 500 nm green photon or a 1 keV X-ray without re-typing the Planck constant.
• • Spectroscopy work: Convert between wavelength, frequency, and electronvolts when reading UV-vis, IR, or Raman spectra.
• • Photodetector sizing: Estimate photons per second reaching a detector from a beam of known power and wavelength.
• • Photoelectric and Compton checks: Compute the incident photon energy that drives the photoelectric effect or Compton scattering kinematics.

Use this calculator whenever you need a quick NIST-traceable answer. It defaults to a 500 nm green photon at 1 W so every output is visible immediately, and it works across the full electromagnetic spectrum from radio waves to gamma rays.

The calculator applies the Planck-Einstein relation E = hν = hc/λ with the exact 2019 SI values for h, c, and the elementary charge. Switch the input mode to match what you measured, and the same result appears in joules, electronvolts, hertz, nanometres, wavenumbers, momentum, and photon flux.

• h: Planck constant, 6.62607015 × 10⁻³⁴ J·s (exact).
• c: Speed of light in vacuum, 299,792,458 m/s (exact).
• ν: Photon frequency in hertz when input mode is frequency.
• λ: Photon wavelength in metres when input mode is wavelength.
• e: Elementary charge, 1.602176634 × 10⁻¹⁹ C, used to convert joules to electronvolts.

When you enter wavelength, the calculator divides h·c by the wavelength in metres. When you enter frequency, it multiplies h by the frequency in hertz. The two routes agree to machine precision, so you can switch modes to cross-check a measured number.

After computing joules, it divides by the elementary charge to give electronvolts. That is the form you usually want for atomic, molecular, and solid-state work where band gaps, work functions, and ionization energies are quoted in eV.

According to NIST CODATA 2018, Speed of light in vacuum is exactly 299,792,458 m/s by the definition of the metre.

According to NIST CODATA 2018, Planck constant is exactly 6.62607015 × 10⁻³⁴ J·s since the 2019 redefinition of the SI.

When you switch from photon energy to particle mass, the same Planck constant and speed of light give the complementary Compton wavelength calculator, which returns λ = h / (m c) for any particle mass.

Four ideas make the photon energy formula simple: a single constant fixes the scale, two equivalent routes give the same number, electronvolts make the result easy to compare with atomic-scale energies, and the energy scales linearly with frequency and inversely with wavelength.

These four ideas are enough to read a photon energy number and tell whether it sits in the radio, microwave, infrared, visible, ultraviolet, X-ray, or gamma-ray range.

A useful mental check: visible light runs from about 1.65 eV (deep red, 750 nm) to about 3.26 eV (violet, 380 nm). Anything below 1.65 eV is infrared; anything above 3.26 eV is ultraviolet.

To see the same Planck-Einstein relation applied to atomic transitions, the Rydberg equation calculator converts the wavelength of a hydrogen line into the photon energy and back.

Use the calculator whenever you know a light source's wavelength or frequency and need the photon energy that drives it. Six short steps cover the most common workflows from spectroscopy to photodetector sizing.

1. 1 Pick the input mode: Choose Wavelength for a colour or spectrum line, and Frequency for a laser spec sheet or an RF source.
2. 2 Enter the wavelength or frequency: Type the number and pick the unit that matches your measurement. Nanometres and terahertz suit visible light; picometres and petahertz suit X-rays.
3. 3 Add beam power for photon flux: Leave power at 1 W for a quick answer or enter your actual beam power to see how many photons per second the source delivers.
4. 4 Read the energy in joules and electronvolts: Joules are the SI answer; electronvolts are the one to compare with work functions, band gaps, and ionization energies.
5. 5 Cross-check the other units: Confirm the implied frequency or wavelength matches your source's data sheet, since the two modes give the same energy to machine precision.
6. 6 Use momentum and flux for detector work: Photon momentum helps with radiation-pressure estimates, and photons-per-second sizes a photodiode or photon-counting experiment.

Mode = Wavelength, λ = 633 nm from a 5 mW HeNe laser. Each photon carries about 3.14 × 10⁻¹⁹ J (1.96 eV). At 5 mW the beam delivers about 1.59 × 10¹⁶ photons per second, which is enough to be detected by a low-noise photodiode or a single-photon counter when attenuated.

When the photon energy drives electrons out of a metal, the photoelectric effect calculator subtracts the work function from the same E = h ν value to give the maximum kinetic energy.

Six practical benefits make a photon energy calculator useful in optics, atomic physics, photochemistry, and quantum information work.

• • Two input modes: Switch between wavelength and frequency without retyping the Planck constant or remembering c. Both modes return identical energies to machine precision.
• • Dual output units: See the answer in joules for SI work and in electronvolts for atomic, molecular, and solid-state physics in one panel.
• • Implied units: Every input shows the implied frequency and wavelength, so a typo or unit error is caught before it propagates into a calculation.
• • Photon momentum and wave number: Get h/λ and 1/λ next to the energy so radiation-pressure, Raman, and IR spectroscopy work does not need a separate tool.
• • Photon flux from a beam power: Enter the beam power and read off photons per second for photodiode sizing, photon-counting experiments, or rate equations.
• • NIST CODATA constants: The calculator uses the exact 2019 SI values for h, c, and e, so results are traceable to NIST without manual lookups.

These benefits make the calculator useful in undergraduate labs, graduate research, and engineering design where you need a quick answer you can trust.

The visible-light, infrared, and ultraviolet ranges all map cleanly through the same relation, so the same tool covers UV-vis, IR, and Raman spectroscopy work.

If your light comes from a hot source rather than a single line, the blackbody radiation calculator integrates the same Planck spectrum over wavelength to give total exitance and peak photon energy.

Five factors decide whether a photon energy number is meaningful for your experiment, and two caveats keep the model honest when the answer looks surprising.

• • The model assumes photons in vacuum. Inside a dispersive medium, the vacuum wavelength gives the right photon energy, but the group velocity changes, and the energy transport picture shifts to Poynting-vector flux.
• • A single-photon energy is not the whole story for a beam. Two beams with the same average power but different photon energies have very different photon flux, polarization, and noise properties, so always check what you actually need.

The same formula cross-checks related calculators on this site, such as the photoelectric effect and Compton wavelength, which both use the Planck-Einstein relation.

For atomic-transition work, the Rydberg equation returns the matching photon energies for hydrogen and hydrogen-like ions, which can then be fed straight back into this calculator.

According to Encyclopaedia Britannica, Photon energy is E = hν = hc/λ, where h is Planck's constant, ν is the frequency, and λ is the wavelength.

When photon energies sit in the X-ray range and you need the matching d-spacing from a diffraction peak, the Bragg's law calculator applies 2 d sin θ = n λ with the same wavelength.