Photon Energy CalculatorFree online other calculator — instant results, no sign-up
Calculate photon energy from wavelength using Planck’s constant.
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About the Photon Energy Calculator
The Photon Energy Calculator converts a wavelength in nanometers into the energy of a single photon in electronvolts using Planck’s constant and the speed of light. At the default wavelength of 550 nm, it returns 2.254258 eV.
- Wavelength (nm)
- The photon’s vacuum wavelength in nanometers (nm), with a default value of 550 nm.
Formula and method
E_eV = (h × c) / [(λ_nm × 10⁻⁹) × J_per_eV]; at λ_nm = 550, E_eV = [(6.62607015 × 10⁻³⁴) × 299792458] / [(550 × 10⁻⁹) × (1.602176634 × 10⁻¹⁹)] = 2.254258 eV, rounded to six decimal places.
- E_eVEnergy of one photon, expressed in electronvolts (eV).
- hPlanck’s constant, exactly 6.62607015 × 10⁻³⁴ joule-seconds (J·s).
- cSpeed of light in vacuum, exactly 299792458 meters per second (m/s).
- λ_nmThe numerical wavelength entered in nanometers; multiplying by 10⁻⁹ converts it to meters.
- J_per_eVEnergy conversion factor, exactly 1.602176634 × 10⁻¹⁹ joules per electronvolt (J/eV).
Convert the entered wavelength from nanometers to meters, then calculate photon energy in joules using E = hc/λ. Divide that energy by the number of joules per electronvolt to obtain eV. For the default input of 550 nm, the displayed result is 2.254258 eV after rounding to six decimal places.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Wavelength550 nm
Results
- Result2.254258 eV
How to use the Photon Energy Calculator
- 1Find the vacuum wavelength of the light you want to evaluate.
- 2Enter that wavelength in the Wavelength (nm) field as a positive number, or leave the default of 550.
- 3Run the calculation to convert wavelength into photon energy.
- 4Read the Result row in eV; with the default input, it shows 2.254258 eV.
- 5If comparing wavelengths, repeat the calculation and note that shorter wavelengths produce higher photon energies.
Reading your result
The Result row gives the energy carried by one photon at the entered wavelength, in electronvolts. For 550 nm, Result = 2.254258 eV. This is not the total energy or power of a light beam: those also depend on how many photons are present or arrive per second.
Limitations
The input must be a finite, positive vacuum wavelength; zero and negative wavelengths are not physically valid here. A wavelength measured inside a material must be converted to its corresponding vacuum wavelength before using this formula with c. The calculator treats the light as having a single wavelength and does not describe a broad spectrum. Displayed decimal places reflect rounding, not the measurement accuracy of the input.
Common questions
What photon energy does the default wavelength of 550 nm produce?+
It produces 2.254258 eV per photon, rounded to six decimal places.
Why does a shorter wavelength give a higher photon energy?+
In E = hc/λ, wavelength is in the denominator. With Planck’s constant and the speed of light fixed, photon energy increases as wavelength decreases.
Can I enter a wavelength measured in glass or water?+
Not directly if it is the wavelength inside that material. Use the corresponding vacuum wavelength; for a known refractive index n at that frequency, λ_vacuum = n × λ_material.
Does brighter light have a higher result in this calculator?+
Not at the same wavelength. Increasing brightness increases the number of photons delivered, while the energy of each photon remains determined by its wavelength.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
Further reading
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Results are estimates for informational purposes and are not financial, medical or legal advice.