Photon Energy, Wavelength & Frequency Calculator

Photon energy is the energy carried by one photon and is linked to its frequency and wavelength. Enter one known value to use this photon wavelength calculator, wavelength-to-energy calculator, or frequency converter.

Calculate from

Enter a positive wavelength; scientific notation and “±” are accepted.

Advanced options and units

Uncertainty uses a first-order relative approximation. For inverse equations, this is most accurate when the uncertainty is small compared with the entered value.

Try a preset

Result summary

4 significant figures

Photon energy
—
Energy calculation
  1. Enter a value to see the calculation.
Wavelength
—
Wavelength calculation
  1. Enter a value to see the calculation.
Frequency
—
Frequency calculation
  1. Enter a value to see the calculation.
Spectral region
— Visible color: —
Wavenumber
— cm⁻¹
Molar photon energy
— kJ/mol
Energy scale
—

Electromagnetic spectrum

Logarithmic wavelength scale from gamma rays to radio. Click, drag, or use arrow keys to choose a wavelength.

No result to classify.

Visible-light inset: 380–750 nm

The calculated value will be described in text; color is never the only indicator.

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How to use the calculator

  1. Choose whether you know wavelength, frequency, or energy.
  2. Enter one positive value and select its unit. Results update after a short pause, or select Calculate.
  3. Read the compact result summary, then expand any calculation to see SI conversion, substitution, intermediate values, and eV conversion.

Inputs may use scientific notation such as 5.45e14. Optional uncertainty may be written as 532 ± 2.

Equations and exact constants

Core equations

E = hf relates energy directly to frequency. f = c/λ relates frequency inversely to vacuum wavelength. Combining them gives E = hc/λ.

The convenient identity E(eV) = 1239.841984/λ(nm) follows from those exact constants.

Constants used

  • c = 299,792,458 m/s exactly
  • h = 6.62607015 × 10⁻³⁴ J·s exactly
  • e = 1.602176634 × 10⁻¹⁹ C exactly
  • NA = 6.02214076 × 10²³ mol⁻¹ exactly

How to calculate photon energy

From wavelength

Convert λ to metres, calculate f = c/λ, then calculate E = hf. In one step, use E = hc/λ. Because this is an inverse relation, halving wavelength doubles photon energy.

From frequency

Convert f to hertz, then calculate E = hf. Wavelength follows from λ = c/f. Frequency and per-photon energy are directly proportional.

Worked examples

1. Wavelength to energy: 532 nm

  1. 532 nm = 532 × 10⁻⁹ m.
  2. f = 299,792,458/(532 × 10⁻⁹) = 5.635 × 10¹⁴ Hz.
  3. E = (6.62607015 × 10⁻³⁴)(5.635 × 10¹⁴) = 3.734 × 10⁻¹⁹ J.
  4. E = 3.734 × 10⁻¹⁹/1.602176634 × 10⁻¹⁹ = 2.331 eV.

2. Frequency to energy: 2.45 GHz

  1. 2.45 GHz = 2.45 × 10⁹ Hz.
  2. E = (6.62607015 × 10⁻³⁴)(2.45 × 10⁹) = 1.623 × 10⁻²⁴ J.
  3. E = 1.013 × 10⁻⁵ eV.
  4. λ = 299,792,458/(2.45 × 10⁹) = 0.1224 m.

3. Energy to wavelength: 50 keV

  1. 50 keV = 50,000 eV = 8.0109 × 10⁻¹⁵ J.
  2. f = E/h = 1.209 × 10¹⁹ Hz.
  3. λ = c/f = 2.480 × 10⁻¹¹ m.
  4. λ = 24.80 pm, in the X-ray region.

How to interpret the spectrum

The spectrum view uses a logarithmic wavelength axis because electromagnetic wavelengths span many powers of ten. From long to short wavelength, the main regions are radio, microwave, infrared, visible, ultraviolet, X-ray, and gamma ray. The boundaries are conventional rather than perfectly sharp; source and application can also affect naming.

Visible light occupies only about 380–750 nm. A color label is shown only inside that interval, while every result receives a text region classification.

Applications and assumptions

Optics commonly uses nm and µm; spectroscopy often uses cm⁻¹; chemistry frequently compares eV per photon with kJ/mol; X-ray and particle physics often uses keV, MeV, or GeV. Molar photon energy is the single-photon energy multiplied by the exact Avogadro constant.

Results describe one photon and a vacuum wavelength. At a boundary, light frequency remains constant. In a medium with refractive index n, phase velocity is v = c/n and wavelength is λmedium = λvacuum/n, so wavelength shortens rather than stretches. This calculator does not model refractive index, dispersion, bandwidth, coherence, intensity, or photon count.

Microwave heating is dielectric heating: an alternating electromagnetic field drives rotation and polarization processes in polar molecules and ions, and energy is dissipated through molecular interactions. It is not accurately described as individual microwave photons simply “exciting water molecules.”

Displayed uncertainty is a first-order propagation approximation. Exact inverse transformations can have asymmetric bounds when uncertainty is large, so use the calculator’s uncertainty output only when the relative uncertainty is small.

Photon energy FAQs

How do I calculate photon energy from wavelength?

Use E = hc/λ. Convert wavelength to metres, multiply the exact values of h and c, and divide by λ.

What does E = hf mean?

Energy equals Planck’s constant times frequency. E is energy per photon in joules, h is 6.62607015 × 10⁻³⁴ J·s, and f (or ν) is frequency in hertz.

Why is E(eV) ≈ 1239.84/λ(nm)?

It is E = hc/λ expressed in eV and nm. Combining the exact SI constants gives E(eV) = 1239.841984/λ(nm), making common optics calculations quick.

How do I convert joules to eV?

Divide by 1.602176634 × 10⁻¹⁹. One electronvolt is exactly that many joules, so 1 J is about 6.241509074 × 10¹⁸ eV.

What energy does a 450 nm photon have?

About 4.414 × 10⁻¹⁹ J, 2.755 eV, or 265.8 kJ/mol. A 450 nm wavelength is generally classified as blue visible light.

Does light frequency change in water?

No. Frequency remains fixed at the boundary; phase velocity and wavelength decrease. For refractive index n, v = c/n and λwater = λvacuum/n.

What does cm⁻¹ mean?

It is spectroscopic wavenumber, equal to 1/λ in centimetres. For example, 500 nm is 20,000 cm⁻¹. Higher wavenumber means higher frequency and photon energy.

What is the difference between energy per photon and kJ/mol?

One is microscopic; the other scales the same energy to a mole of photons. Multiply joules per photon by 6.02214076 × 10²³ mol⁻¹ and divide by 1000 to get kJ/mol.

Methodology and sources

The calculator converts the selected input to SI units, applies E = hf and f = c/λ using JavaScript number precision, then converts the outputs. Defining constants are exact; only displayed results are rounded to the selected number of significant figures. Results assume a single photon in vacuum because no refractive-index input is provided.

Last reviewed: July 18, 2026. Published by Starlight Robotics. No external scientific reviewer is claimed.

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