Wavelength to Energy Calculator
This is Omni's wavelength to energy calculator, a tool that instantly calculates a photon's energy from its wavelength. By using Planck's equation, this tool will help you determine a photon's energy in joules (J), electronvolts (eV), or its multiples.
In this article, you'll also find the Planck equation, a stepbystep guide on how to calculate the energy from the wavelength of a photon and how to get this result in joules or electronvolts.
The wavelength to energy formula – Planck's equation
Planck's equation, also known as Planck's relation, is an expression that allows you to define a photon's energy E in terms of its wave properties. Planck's relation states that the energy is directly proportional to its frequency $f$:
Or inversely proportional to wavelength $\lambda$, by recalling the relationship between frequency and wavelength, $f = c / \lambda$:
where:
 $E$ – Photon energy;
 $h$ – Planck's constant, 6.6261 x 10^{34} J·s or 4.1357 x 10^{15} eV·s;
 $c$ – Speed of light, 299792458 m/s;
 $\lambda$ – Wavelength; and
 $f$ – Photon frequency.
Notice that if a photon's frequency $f$ or wavelength $\lambda$ are known, you can directly determine its energy $E$ since the other elements in the equation are constants.
🙋 The energy of a photon is commonly expressed using the unit electronvolt (eV), but it can also be expressed in other energy units, such as joules (J).
How do I calculate energy from wavelength?
To calculate a photon's energy from its wavelength:
 Multiply Planck's constant, 6.6261 × 10⁻³⁴ J·s by the speed of light, 299792458 m/s.
 Divide this resulting number by your wavelength in meters.
 The result is the photon's energy in joules.
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FAQ
How do I find the energy in joules given the wavelength?
To find the energy in joules given the wavelength of a photon:
 Use Planck's equation E = h x c / λ and substitute the values of the wavelength (λ), Planck's constant in joules (h = 6.6261 × 10⁻³⁴ J·s), and speed of light (c = 299792458 m/s).
 With these units, you'll get an energy result in joules (J).
 That's it!
How do I convert wavelength to energy in eV?
In order to convert a wavelength to energy in electronvolts (eV):

Utilize Planck's energy equation E = h × c / λ.

Substitute the values of the wavelength (λ), Planck's constant (h = 6.6261 × 10⁻³⁴ J·s), and speed of light (c = 299792458 m/s).

You'll get a result in joules (J).

To go from joules (J) to electronvolts (eV), use the conversion factor 1eV = 1.602176565 × 10⁻¹⁹ J.

Finally, to express your result in electronvolts, divide the energy in joules by the conversion factor:
E [J] / 1.602176565 e⁻¹⁹ J/eV = E [eV].
How do I calculate the energy of a photon of wavelength 3.5 μm?
To calculate the energy of a photon of wavelength 3.5 μm:

Employ Planck's energy equation, E = h × c / λ.

Use the values of the wavelength λ = 3.5 μm, Planck's constant h = 6.6261 × 10⁻³⁴ J·s and speed of light c = 299792458 m/s.

Substitute into Planck's equation, E = 3.5 μm × (6.6261 × 10⁻³⁴ J·s) × (299792458 m/s).

After performing the required operations, you'll get that the energy value is E = 354.242 meV.
What is the energy of a 100 nm photon?
The energy of a 100 nm photon is 12.39847 eV or 1.99 × 10⁻¹⁸ J. To get this result:

Employ Planck's equation, E = h × c / λ:

Where λ = 3.5 μm is the wavelength, h = 6.6261 × 10⁻³⁴ J⋅s Planck's constant and c = 299792458 m/s the speed of light.

Replace, E = 3.5 μm × (6.6261 × 10⁻³⁴ J·s) × (299792458 m/s) = 12.39847 eV.

To express the result in joules, apply the conversion factor 1eV = 1.602176565 × 10⁻¹⁹ J. Therefore:
E = 12.39847 eV x (1.602176565 x 10⁻¹⁹ J/eV) = 1.99 × 10⁻¹⁸ J.