Photon Energy Calculator
The energy of a single photon from its wavelength or frequency — in joules and electronvolts, with the part of the spectrum it belongs to.
How much energy one particle of light carries.
How the photon energy calculator works
E = hf, and since c = fλ, also E = hc/λ. Energy is inversely proportional to wavelength: blue light carries more per photon than red, and ultraviolet more than either.
That inverse relation is the whole of photochemistry. A photon either has enough energy to break a bond or it does not, and no amount of dim red light will do what a little ultraviolet does — which is why UV damages skin and infrared merely warms it.
Formula: E = hf = hc/λ
Worked examples
| Inputs | Photon energy | Note |
|---|---|---|
| Green light at 550 nm | 2.2543 eV | 2.25 eV |
| Ultraviolet at 250 nm | 4.9594 eV | 4.96 eV — enough to break bonds |
| A microwave photon | 0 eV | 10 µeV — a million times weaker |
FAQFrequently asked questions
How much energy is in a photon of visible light?
Between about 1.65 eV (red, 750 nm) and 3.1 eV (violet, 400 nm).
Why does UV damage skin but infrared does not?
Because a UV photon carries enough energy to break chemical bonds and an infrared one does not. Intensity cannot substitute — this is the photoelectric effect that won Einstein his Nobel.
What is an electronvolt?
The energy an electron gains crossing one volt — 1.602 × 10⁻¹⁹ J. It is the natural unit at atomic scales.
How many photons in a joule of green light?
About 2.8 × 10¹⁸. A single photon is unimaginably small on a human energy scale.
Does a photon have mass?
No rest mass, but it carries momentum p = E/c — which is what makes solar sails and radiation pressure possible.
Where these figures come from
- NIST — CODATA 2018 fundamental physical constants — G, g₀, R, c
- NIST Special Publication 811 — Guide for the use of the International System of Units — unit conversions
- The Engineering ToolBox — material properties — specific heats, expansion coefficients, densities
- National Institute of Standards and Technology — the US measurement authority
Last checked: September 2026. Constants are the CODATA 2018 values; formulas are the standard textbook forms.