Convert wavelength to frequency for any EM radiation. Supports pm to km, 8 wavelength units, photon energy, wave number, visible color identification. Includes spectrum visual and conversion tables.
The frequency of electromagnetic radiation is determined by its wavelength through the universal relationship f = c/λ, where c is the speed of light in vacuum (299,792,458 m/s). This conversion is pivotal in optics, spectroscopy, telecommunications, and quantum physics. Knowing the frequency from a wavelength tells you the photon energy (E = hf), which determines the radiation's interaction with matter.
In a medium with refractive index n, the relationship becomes f = c/(nλ_medium), but since frequency doesn't change between media, the vacuum wavelength is λ_vac = nλ_medium. Spectroscopists often work with wave number (cm⁻¹) = 10,000/λ(μm), which is proportional to energy and convenient for infrared spectroscopy.
This calculator accepts wavelength in 8 units from picometers to kilometers plus angstroms. It outputs frequency in the most readable unit, photon energy in eV and joules, wave number, and period. For visible wavelengths (380-700 nm), it identifies the color and shows the position on a rainbow gradient. Full conversion tables for both wavelength and frequency units are provided.
Spectroscopists, optics engineers, and physicists routinely convert between wavelength, frequency, energy, and wave number. Each sub-field has its preferred units: nm for visible, μm for infrared, cm⁻¹ for spectroscopy, eV for quantum transitions. This calculator converts among all of them in one step and identifies visible colors automatically. Keep these notes focused on your operational context.
f = c / λ = c / (n × λ_medium) Where: c = 299,792,458 m/s n = refractive index (1 for vacuum) λ_vac = n × λ_medium Photon energy: E = hf = hc/λ h = 6.626 × 10⁻³⁴ J·s E(eV) = E(J) / 1.602 × 10⁻¹⁹ Wave number: ν̃ = 1/λ (m⁻¹) or 10⁷/λ(nm) cm⁻¹
Result: f = 545.08 THz, E = 2.254 eV
Green light at 550 nm: f = 299,792,458 / (550 × 10⁻⁹) = 5.451 × 10¹⁴ Hz = 545.08 THz. Energy = 6.626e-34 × 5.451e14 = 3.61e-19 J = 2.254 eV. Wave number = 18,182 cm⁻¹. This is near the peak sensitivity of the human eye.
Spectroscopy — the study of matter's interaction with electromagnetic radiation — relies entirely on the wavelength-frequency-energy relationship. Absorption spectroscopy measures which wavelengths a sample absorbs (identifying bonds and elements). Emission spectroscopy measures which wavelengths a sample emits when excited. Raman spectroscopy measures wavelength shifts caused by molecular vibrations. In every case, converting wavelength to energy reveals the quantum transitions occurring in the sample.
Fiber optic networks use specific wavelength bands where silica glass has minimum loss: the O-band (1260-1360 nm), C-band (1530-1565 nm), and L-band (1565-1625 nm). Dense wavelength division multiplexing (DWDM) packs 80-160 channels in the C-band alone, each separated by 50-100 GHz (≈0.4-0.8 nm). Converting between wavelength and frequency is essential for channel planning and filter design.
Astronomers use wavelength-to-frequency conversion to determine the composition and motion of stars and galaxies. Absorption and emission lines at known wavelengths identify elements. Doppler shift changes these wavelengths: approaching objects are blue-shifted (shorter λ), receding objects are red-shifted (longer λ). Cosmological redshift, where spacetime expansion stretches wavelengths, reveals the distance and age of distant galaxies.
f(THz) = 299,792.458 / λ(nm). For 550 nm: 299,792.458 / 550 = 545.08 THz. For 1550 nm: 299,792.458 / 1550 = 193.41 THz. This calculator handles this automatically.
Wave number (cm⁻¹) = 10,000 / λ(μm). It is proportional to photon energy, making it convenient for spectroscopy. Energy (eV) = wave number (cm⁻¹) × 1.2398 × 10⁻⁴. Unlike wavelength, wave number is additive for energy calculations.
Vacuum wavelength is the universal reference because frequency doesn't change between media. A 1550 nm fiber signal has λ_vac = 1550 nm regardless of whether it is in air, glass, or vacuum. The in-medium wavelength depends on the material's refractive index.
Inversely: E = hc/λ. Shorter wavelength = higher energy. A 400 nm violet photon (3.1 eV) has 75% more energy than a 700 nm red photon (1.77 eV). X-rays at 0.1 nm have ~12,400 eV — enough to ionize any atom.
Bright green. This is the wavelength of the ubiquitous green laser pointer (frequency-doubled Nd:YAG). It appears very bright because the human eye's peak sensitivity is near 555 nm.
Yes. Enter the wavelength in meters or cm and select the appropriate unit. For example, FM radio at 3 m wavelength → 100 MHz. For radio work, the wavelength calculator (frequency → wavelength direction) may be more natural.