CALCULATOR

Photon energy–wavelength conversion

Convert between wavelength and photon energy.

I. Wavelength to photon energy

Input

Wavelength Unit

Output

Energy unit for output Decimal places in output

Result
Input (wavelength)	Output (energy)
—	—

II. Photon energy to wavelength

Input

Photon energy Unit

Output

Wavelength unit for output Decimal places in output

Result
Input (energy)	Output (wavelength)
—	—

About this calculator

You can choose the input and output units from the dropdown menus. For example, to enter a wavelength of 550 nm, set the unit to “nm” and enter “550” for the wavelength.

The photon energy input unit “×10^(-19) [J]” lets you omit the 10⁻¹⁹ J factor when entering a value. For example, to enter 3.972 × 10⁻¹⁹ J, set the unit to “×10^(-19) [J]” and enter “3.972” as the input value.

Output values are shown in decimal notation. You can specify the number of decimal places in the output. If a positive result rounds to zero at the specified number of decimal places, a warning is displayed below the result.

The wavelength λ used in this calculation is the vacuum wavelength. If you are working with a wavelength in a medium, convert it to the vacuum wavelength using the refractive index before entering it.

Method

E = hc / λ

Here, the speed of light in vacuum is c = 2.99792458 × 10⁸ m/s, the Planck constant is h = 6.62607015 × 10⁻³⁴ J·s, and the conversion uses 1 eV = 1.602176634 × 10⁻¹⁹ J.

Sources of constants

The speed of light in vacuum c, the Planck constant h, and the elementary charge e are based on NIST documentation, as exact values that define the SI.

NIST SP 330, Section 2: The International System of Units (SI)
NIST CODATA Recommended Values of the Fundamental Physical Constants: 2022
Mohr, P. J.; Newell, D. B.; Taylor, B. N.; Tiesinga, E., “CODATA recommended values of the fundamental physical constants: 2022,” Rev. Mod. Phys. 97, 025002 (2025). DOI: 10.1103/RevModPhys.97.025002

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