Quantum & EM Tool Physics & Engineering

Photon Energy Calculator

Convert photon wavelength or frequency to energy in Joules, electronvolts and kJ/mol. Explore photon momentum and identify where a wavelength or frequency lies in the electromagnetic spectrum from gamma rays to radio waves.

Wavelength & frequency Energy in J & eV Photon momentum EM spectrum region

Multi-Mode Photon Energy & EM Spectrum Calculator

Use the tabs to convert wavelength or frequency to photon energy, switch between Joules and eV, compute energy per mole and photon momentum, and classify radiation into gamma, X-ray, ultraviolet, visible, infrared, microwave or radio regions.

This mode uses E = h c / λ and f = c / λ with Planck's constant and the speed of light in vacuum. Results are given per photon and per mole of photons.

This mode uses E = h f and λ = c / f. Large frequencies correspond to very energetic photons (X-rays and gamma rays), while low frequencies correspond to radio waves.

Use this tab to convert photon energy among Joules per photon, electronvolts and kilojoules per mole. The conversion uses the elementary charge and Avogadro constant.

Used when calculation mode is set to wavelength.
Enter energy in eV when using energy mode.

Photon momentum is given by p = h / λ or equivalently p = E / c. Although photons are massless, they still carry momentum and can exert radiation pressure.

The electromagnetic spectrum is divided into regions by wavelength or frequency. Boundaries are approximate and may vary slightly between references, but the relative ordering from gamma rays to radio waves is consistent.

Photon Energy Calculator – From Wavelength and Frequency to Energy

In quantum physics, light behaves both as a wave and as a stream of particles called photons. Each photon carries a discrete amount of energy that depends only on its frequency (or equivalently on its wavelength in vacuum). This Photon Energy Calculator lets you convert between wavelength, frequency and energy, while also providing photon momentum and a basic electromagnetic spectrum classification.

Key Photon Energy Formulas

The fundamental relation for photon energy is:

  • Energy–frequency: E = h f
  • Frequency–wavelength: f = c / λ
  • Energy–wavelength: E = h c / λ

Here, E is the energy of a photon, h is Planck's constant, f is frequency, c is the speed of light in vacuum and λ is wavelength. When wavelength decreases, frequency and photon energy both increase.

Mode 1 – Wavelength to Photon Energy

In the wavelength mode you specify a wavelength in meters, nanometers, micrometers or Angstroms. The calculator converts that value into meters, applies E = h c / λ and reports:

  • Photon energy in Joules per photon (J)
  • Photon energy in electronvolts (eV)
  • Energy in kilojoules per mole of photons (kJ/mol)
  • Frequency in hertz from f = c / λ
  • Optional wavenumber in cm⁻¹, commonly used in spectroscopy

Mode 2 – Frequency to Photon Energy

In the frequency mode you enter a frequency in Hz, kHz, MHz, GHz or THz. The tool converts it to hertz, computes the photon energy using E = h f and then finds the corresponding wavelength via λ = c / f. This is useful when you know the frequency of a laser, radio transmitter or X-ray source and want the associated photon energy.

Mode 3 – Photon Energy Unit Converter

Many disciplines express photon energy in different units:

  • Joules per photon (J)
  • Electronvolts (eV)
  • Kilojoules per mole (kJ/mol)

The energy converter tab takes a single input value in any of these units and converts it to the other two, using the exact values of the elementary charge and Avogadro constant. This is especially handy when moving between quantum and chemical or spectroscopic contexts.

Mode 4 – Photon Momentum

Although photons have no rest mass, they still carry momentum and can exert pressure on surfaces. The momentum p of a photon can be expressed in two equivalent ways:

  • From wavelength: p = h / λ
  • From energy: p = E / c

The momentum tab lets you compute p from either wavelength or energy. The calculator returns momentum in kilogram meter per second (kg·m/s) and also shows the corresponding photon energy and wavelength that were used in the calculation.

Mode 5 – Electromagnetic Spectrum Classification

The electromagnetic (EM) spectrum is the full range of photon energies and wavelengths, from very high-energy gamma rays to very long-wavelength radio waves. In broad terms:

  • Gamma rays: extremely short wavelengths, highest photon energies
  • X-rays: slightly longer than gamma rays, used in medical imaging
  • Ultraviolet (UV): shorter than visible light, causes sunburn and many fluorescence effects
  • Visible light: the narrow band detectable by the human eye
  • Infrared (IR): emitted strongly by warm objects, used in thermal imaging and remote controls
  • Microwaves: centimeter to millimeter wavelengths, used in communication and microwave ovens
  • Radio waves: long wavelengths used for broadcasting and wireless communication

The EM spectrum tab takes either wavelength or frequency, converts between the two, computes photon energy and then assigns an approximate region label. The exact numerical boundaries between regions vary between sources, but the ordering and trends are consistent.

Using the Photon Energy Calculator Effectively

  • Use Wavelength → Energy when you know the wavelength of a laser or LED and need its photon energy.
  • Use Frequency → Energy for RF, microwave or higher-frequency sources specified in hertz.
  • Use the Energy Unit Converter to switch between Joules, eV and kJ/mol when reading papers or datasheets.
  • Use Photon Momentum when studying radiation pressure, solar sails or photon–matter interactions.
  • Use the EM Spectrum Identifier to quickly see whether a photon is UV, visible, IR and how energetic it is.

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Photon Energy FAQs

Frequently Asked Questions About Photon Energy

Quick answers about wavelength, frequency, energy and the electromagnetic spectrum.

Photon energy is proportional to frequency (E = h f), and frequency is inversely proportional to wavelength (f = c / λ). When wavelength becomes shorter, frequency increases, which in turn increases photon energy. That is why ultraviolet and X-rays are more energetic and potentially more damaging than visible or infrared light.

Joules measure absolute energy in SI units, electronvolts express energy on an atomic or particle scale and kilojoules per mole express energy per Avogadro's number of photons, which is convenient in chemistry and spectroscopy. All three quantify the same underlying energy but at different scales.

Photon energy depends only on frequency, which remains constant as light passes from one medium to another. Wavelength shortens inside a medium with refractive index greater than one, but the photon energy itself stays the same because the frequency does not change at the boundary in this ideal model.

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