# 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 step-by-step 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.

## More wavelength and energy calculators!

If you enjoyed using this tool and you'd like to get more information about a photon's energy and its wavelength, we invite you to visit more of our related tools:

## 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 electrovolts, divide the energy in joules by the conversion factor:
`E [J] / 1.602176565e⁻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**,`E = 12.39847 eV x (1.602176565 x 10⁻¹⁹ J/eV) = 1.99 × 10⁻¹⁸ J`

.