What formula does this calculator use?

The calculator uses E = hf for frequency input and E = hc/λ for wavelength input, where h = 6.62607015 × 10⁻³⁴ J·s (Planck's constant, exact SI value), c = 299,792,458 m/s (speed of light, exact SI value), f is frequency in hertz, and λ is wavelength in meters.

What is an electron volt (eV) and why is it used?

An electron volt is the kinetic energy gained by one electron accelerated through a 1-volt potential difference, equal to approximately 1.602 × 10⁻¹⁹ J. It is the standard unit for photon and particle energies in atomic physics because joule values are inconveniently small (e.g., a visible photon is only ~10⁻¹⁹ J but ~2 eV).

What is kJ/mol and when is it useful?

kJ/mol is the energy of one mole (6.022 × 10²³) of photons. It is the unit chemists prefer because thermodynamic and bond-energy data are also tabulated per mole. Ultraviolet photons (~400 nm) carry about 300 kJ/mol — comparable to typical chemical bond energies.

What EM spectrum band does my photon belong to?

The calculator automatically classifies your photon into a spectrum band (radio, microwave, infrared, visible, ultraviolet, X-ray, or gamma) based on its vacuum wavelength. For visible light it also reports the approximate color.

Why does medium not affect photon energy?

Photon energy E = hf depends only on frequency. When light enters a denser medium, its speed and wavelength both decrease by the refractive index n, but frequency is unchanged, so energy is unchanged. This calculator assumes vacuum (n = 1) for wavelength inputs, which gives the correct photon energy regardless of medium.

Photon Energy Calculator

Name: Photon Energy Calculator
Availability: InStock
Author: Nham Vu

Enter a wavelength or frequency to instantly compute photon energy in joules, eV, and kJ/mol.

Photon Input

Input Type

Wavelength

Quick Examples

Enter a wavelength or frequency to calculate photon energy

Results shown in J, eV, and kJ/mol

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Summary

Enter a wavelength or frequency to instantly compute photon energy in joules, eV, and kJ/mol.

How it works

Choose your input type: Wavelength or Frequency.
Enter a numeric value and select the appropriate unit.
Click Calculate to compute the photon energy.
Results appear in joules (J), electron volts (eV), and kilojoules per mole (kJ/mol).
Use the Copy button next to any result to copy it to your clipboard.
Click Reset to clear all fields and start a new calculation.

Use cases

Physics and chemistry students solving E = hf or E = hc/λ problems.
Spectroscopy researchers converting wavelength measurements to energy.
Engineers sizing photovoltaic cells by comparing photon energy to band gaps.
Educators demonstrating the quantum relationship between light and energy.
Chemists calculating molar photon energy (kJ/mol) for photochemical reactions.
Anyone needing a quick joules-to-eV conversion for visible or UV light.

Frequently Asked Questions

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Last updated: 2026-05-23 · Reviewed by Nham Vu