Energy to Wavelength Calculator

Use the Planck–Einstein relation: λ = hc/E, where h is Planck's constant (6.626 × 10⁻³⁴ J·s), c is the speed of light (3 × 10⁸ m/s), and E is the photon energy in joules. Divide hc by the energy to get the wavelength in meters, then convert to your preferred unit. For energy in eV, first multiply by 1.602 × 10⁻¹⁹ to convert to joules.

Rearrange the same formula: E = hc/λ. Plug in Planck's constant h = 6.626 × 10⁻³⁴ J·s and the speed of light c = 3 × 10⁸ m/s, then divide by the wavelength in meters. The result is energy in joules; divide by 1.602 × 10⁻¹⁹ to convert to electronvolts (eV).

When wavelength decreases, energy increases. Because energy and wavelength are inversely proportional (E = hc/λ), a shorter wavelength means the photon oscillates more rapidly and carries more energy. This is why X-rays and gamma rays, which have very short wavelengths, are far more energetic than visible light or radio waves.

Energy decreases as wavelength increases. The inverse relationship (E ∝ 1/λ) means that longer-wavelength photons — such as infrared or radio waves — carry significantly less energy than shorter-wavelength photons like ultraviolet or X-rays.

The Planck–Einstein relation (E = hf) links a photon's energy E to its frequency f through Planck's constant h (6.626 × 10⁻³⁴ J·s). Combined with the wave speed equation (c = fλ), it gives the energy-to-wavelength formula E = hc/λ, which is the foundation of this calculator.

Visible light wavelengths are most commonly expressed in nanometers (nm), where 1 nm = 10⁻⁹ m. Atomic-scale and X-ray wavelengths are often given in angstroms (Å, where 1 Å = 0.1 nm). Radio and microwave wavelengths may be expressed in meters or centimeters. This calculator lets you choose nanometers, meters, micrometers, or angstroms.

The electromagnetic spectrum is divided into regions by wavelength: gamma rays (<0.01 nm), X-rays (0.01–10 nm), ultraviolet (10–400 nm), visible light (400–700 nm), infrared (700 nm–1 mm), microwaves (1 mm–10 cm), and radio waves (>10 cm). This calculator automatically identifies and displays the spectral region for your calculated wavelength.

Divide the energy in kJ/mol by Avogadro's number (6.022 × 10²³ mol⁻¹) and multiply by 1000 to get joules per photon. For example, 200 kJ/mol ÷ 6.022 × 10²³ × 1000 ≈ 3.32 × 10⁻¹⁹ J per photon. This calculator handles that conversion automatically when you select kJ/mol as the input unit.