# Photon Energy Calculator

> Find the energy of a photon from its wavelength, frequency or energy in eV with E = hf = hc/λ, using the exact SI values of h, c and the elementary charge.

Category: Science & engineering · Applies to: Worldwide · Last updated: 2026-10-29
Interactive calculator: https://calculators.geekmidst.com/calculators/photon-energy-calculator

A photon’s energy depends only on its frequency: E = h × f = h × c ÷ λ. Shorter wavelengths carry more energy per photon.

Also called: Planck relation calculator, Wavelength to electronvolt converter.

## Inputs
- Start from (options: Wavelength, Frequency, Energy (eV); default wavelength)
- Wavelength (in vacuum) (default 500)
- Wavelength unit (options: nm, µm, mm, cm, m, km; default nm)
- Frequency (default 600)
- Frequency unit (options: Hz, kHz, MHz, GHz, THz; default THz)
- Photon energy (unit eV; default 2)

## Results
- Energy per photon
- Energy per photon (joules)
- Energy per mole of photons
- Wavelength
- Frequency

## Formula

```
E = h × f = h × c ÷ λ;  E(eV) = E(J) ÷ e;  E per mole = E × N_A
```

Where:
- h: Planck constant, 6.62607015 × 10⁻³⁴ J·s (exact)
- c: speed of light, 299,792,458 m/s (exact)
- e: elementary charge, 1.602176634 × 10⁻¹⁹ C (exact)
- N_A: Avogadro constant, 6.02214076 × 10²³ mol⁻¹ (exact)
- λ: vacuum wavelength
- f: frequency

## Worked example
1. hc = 6.62607015 × 10⁻³⁴ × 299,792,458 = 1.98645 × 10⁻²⁵ J·m.
2. E = 1.98645 × 10⁻²⁵ ÷ (500 × 10⁻⁹ m) = 3.97289 × 10⁻¹⁹ J.
3. E = 3.97289 × 10⁻¹⁹ ÷ 1.602176634 × 10⁻¹⁹ = 2.4797 eV.

**Result:** A 500 nm (green) photon carries about 2.48 eV, or 3.97 × 10⁻¹⁹ J.

## What the result means

A handy shortcut is E (eV) ≈ 1239.84 ÷ λ (nm). Compare the result with a material’s band gap or work function to see whether light of that colour can excite electrons or eject them (the photoelectric effect).

## Assumptions and limits
- Wavelength is the vacuum wavelength. All four constants are the exact defining values of the 2019 SI.
- In a medium the wavelength is shorter but the photon energy is unchanged; enter the vacuum wavelength or the frequency.

## Questions

### Why is energy per mole useful?

It puts photon energies on the same scale as chemical bond energies (typically 150–1,000 kJ/mol), showing which light can break which bonds.

### What is 1 eV in wavelength?

About 1,239.84 nm, in the near infrared.

## Sources
- [NIST (National Institute of Standards and Technology)](https://www.nist.gov/)

## Related calculators
- [Frequency and Wavelength Calculator](https://calculators.geekmidst.com/calculators/frequency-wavelength-calculator)
- [Thin Lens Equation Calculator](https://calculators.geekmidst.com/calculators/optical-lens-equation-calculator)

Source: GM¹X CalcVerse — https://calculators.geekmidst.com/calculators/photon-energy-calculator