Frequency of Light Calculator — Wavelength to Frequency, Energy & Period
Enter a wavelength in nanometres to get the frequency in THz, photon energy in eV, period in femtoseconds and wavenumber — covering UV, visible, and infrared light.
nm
Oscillations per second (1 THz = 10¹² Hz)
- 1
Convert wavelength to metres
550 nm × 10⁻⁹ = 0.000000551 nm = 10⁻⁹ m - 2
Frequency = c / λ
299 792 458 ÷ 0.00000055 = 545,077,196,363,636.3 Hz - 3
Frequency in THz
545,077,196,363,636.3 ÷ 10¹² = 545.0772
How does this calculator work?
f = c / λ where c = 299,792,458 m/s and λ must be in metres (so nm × 10⁻⁹). T = 1/f (period in seconds). E = h × f with h = 6.626 × 10⁻³⁴ J·s; divide by 1.602 × 10⁻¹⁹ to get eV. Wavenumber = 1/λ(cm). Visible light is 380–750 nm (400–790 THz, 1.65–3.26 eV).
Formula
How this is calculated
Light (and all electromagnetic radiation) travels through a vacuum at c = 299,792,458 m/s. Its wavelength λ and frequency f are linked by c = f × λ, so knowing either one determines the other. This calculator takes the wavelength in nanometres (1 nm = 10⁻⁹ m), converts it to metres, and divides c by it to give the frequency in hertz. The result is shown in THz (terahertz, 10¹² Hz) because visible-light frequencies (400–750 nm) fall in the 400–750 THz range.
The period T = 1/f is the time for one complete oscillation, expressed here in femtoseconds (1 fs = 10⁻¹⁵ s) — visible light completes one cycle in roughly 1.3–2.5 fs. Photon energy is calculated from Planck's relation E = h × f, where h = 6.626 × 10⁻³⁴ J·s is Planck's constant; the result is shown in electron-volts (eV) because that unit is most commonly used in atomic and optical physics. Visible photons carry about 1.65–3.26 eV. Wavenumber ν̃ = 1/λ (with λ in centimetres) is the unit used in IR spectroscopy and Raman spectroscopy.
The speed of light used is the exact SI-defined value c = 299,792,458 m/s (2018 redefinition). The calculator classifies the wavelength into its spectral region (UV, visible colours, NIR, IR, etc.) for quick reference. All results assume propagation in vacuum — in a medium with refractive index n, the wavelength shortens to λ/n but the frequency stays the same.
Frequently asked questions
Because c = f × λ and c is constant in vacuum. If λ decreases (shorter waves), f must increase proportionally to keep their product equal to c. Violet light (~400 nm) oscillates twice as fast as red light (~800 nm) even though both travel at the same speed.
A photon carries energy E = hf. In electron-volts, visible photons carry about 1.65–3.26 eV. This unit is convenient because atomic electron transitions that emit or absorb light also occur on the eV scale: a hydrogen atom's Lyman-alpha photon (121.6 nm) carries 10.2 eV, while a typical green photon (550 nm) carries 2.25 eV.
No — the frequency (and energy) of a photon is unchanged when it crosses an interface. What changes is the wavelength: in a medium with refractive index n the wavelength shortens to λ/n and the speed drops to c/n. This is why prisms spread white light into colours — different wavelengths slow by different amounts in glass.
Also known as
TG we-Calculate Editorial Team. (2026). Frequency of Light Calculator — Wavelength to Frequency, Energy & Period [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/frequency-of-light-calculator
TG we-Calculate Editorial Team. "Frequency of Light Calculator — Wavelength to Frequency, Energy & Period." TG we-Calculate. 2026. https://we-calculate.com/calculator/frequency-of-light-calculator.
TG we-Calculate Editorial Team, "Frequency of Light Calculator — Wavelength to Frequency, Energy & Period," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/frequency-of-light-calculator
@misc{wecalculate_frequency_of_light_calculator, title = {Frequency of Light Calculator — Wavelength to Frequency, Energy & Period}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/frequency-of-light-calculator}}, year = {2026}, note = {TG we-Calculate} }
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