Wavelength to Frequency Calculator
Convert between wavelength, frequency and photon energy (λ = v/f, E = hf) with exact CODATA constants, auto-scaled units from km to pm, and the spectrum band named.
Wavelength to Frequency Calculator: with the default inputs, wavelength is 550 nm.
- Frequency
- 545.0772 THz
- Photon energy
- 2.2543 eV (3.6117 × 10⁻¹⁹ J)
- Spectrum band
- Visible — green
- Period
- 1.8346 fs1 ÷ f — time for one cycle.
- Wavenumber (cm⁻¹)
- 18,181.8181 ÷ λ in cm, the spectroscopist's unit.
- Wavelength (nm)
- 550
- Frequency (Hz)
- 545,077,196,363,636.3
Assumptions
- Vacuum speed of light unless you change the medium speed.
- Spectrum band edges are the conventional ones and are judged by vacuum wavelength.
- Photon energy is per photon (E = hf); beam power is not considered.
| Band | Vacuum wavelength | Frequency | Photon energy | Where you meet it |
|---|---|---|---|---|
| Radio | > 1 m | < 300 MHz | < 1.24 µeV | AM/FM, TV, marine VHF |
| Microwave | 1 m – 1 mm | 300 MHz – 300 GHz | 1.24 µeV – 1.24 meV | Wi-Fi, radar, microwave ovens, 5G |
| Far infrared | 1 mm – 50 µm | 300 GHz – 6 THz | 1.24 – 24.8 meV | Thermal imaging of room-temperature objects |
| Mid / near infrared | 50 µm – 750 nm | 6 – 400 THz | 24.8 meV – 1.65 eV | Remote controls, fibre optics, night vision |
| Visible | 750 – 380 nm | 400 – 789 THz | 1.65 – 3.26 eV | Everything your eyes do |
| Ultraviolet | 380 – 10 nm | 789 THz – 30 PHz | 3.26 eV – 124 eV | Sunburn (UV-A/B), sterilizing lamps (UV-C) |
| X-ray | 10 nm – 10 pm | 30 PHz – 30 EHz | 124 eV – 124 keV | Medical imaging, crystallography |
| Gamma ray | < 10 pm | > 30 EHz | > 124 keV | Radioactive decay, cosmic sources |
Band edges are conventional and overlap between sources; the ranges above are the common ones. Your wave falls in the visible — green band.
How this is worked out
The formula
λ = v ÷ f (v = c = 299,792,458 m/s in vacuum) E = h × f = h c ÷ λ h = 6.62607015 × 10⁻³⁴ J·s 1 eV = 1.602176634 × 10⁻¹⁹ J λ = wavelength (m), f = frequency (Hz), E = photon energy (J) Handy: E(eV) ≈ 1239.84 ÷ λ(nm)
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- Start from
- Choose one of 3 options.Wavelength → frequency & photon energy · Frequency → wavelength & photon energy · Photon energy → wavelength & frequency
- Wavelength (λ)
- A number.0 or more · defaults to 550
- Wavelength unit
- Choose one of 7 options.pm (picometers) · nm (nanometers) · µm (micrometers) · mm · cm · m · km
- Frequency (f)
- A number.0 or more · defaults to 100
- Frequency unit
- Choose one of 6 options.Hz · kHz · MHz · GHz · THz · PHz
- Photon energy (E)
- A number.0 or more · defaults to 2.5
- Energy unit
- Choose one of 5 options.meV · eV · keV · MeV · J
- Wave speed in the medium(under More options)
- Default is c in vacuum. Light in glass ≈ 2.0 × 10⁸ (c ÷ n); sound in air at 20 °C = 343; sound in water ≈ 1,480.0 or more · defaults to 299792458
What you get back
- Wavelengthmain answer
- Frequency
- Photon energy
- Spectrum band
- Period
- 1 ÷ f — time for one cycle.
- Wavenumber (cm⁻¹)
- 1 ÷ λ in cm, the spectroscopist's unit.
- Wavelength (nm)
- Frequency (Hz)
What this assumes
- Vacuum speed of light unless you change the medium speed.
- Spectrum band edges are the conventional ones and are judged by vacuum wavelength.
- Photon energy is per photon (E = hf); beam power is not considered.
About this calculator
Every wave obeys v = fλ: speed equals frequency times wavelength. For light in vacuum the speed is the exact constant c = 299,792,458 m/s, so wavelength and frequency are just two descriptions of the same wave — and Planck's relation E = hf turns either into the energy of a single photon. Enter whichever one you know, in units from picometers to kilometers or hertz to petahertz, and the calculator gives the other two, names the part of the spectrum you are in, and shows the arithmetic with the exact CODATA constants.
Reading the results
- Results are auto-scaled, so 550 nm light shows as 545.1 THz and 2.254 eV rather than a wall of zeros; the plain nm and Hz values are listed underneath for copying.
- Spectrum band follows the conventional edges: radio above 1 m, microwave 1 mm–1 m, infrared to 750 nm, visible 380–750 nm (with the colour named), ultraviolet to 10 nm, X-rays to 10 pm, gamma below.
- Wavenumber (cm⁻¹) is what infrared spectroscopists quote: 1 ÷ λ in centimeters.
Intuition worth keeping
E(eV) ≈ 1240 ÷ λ(nm) is a one-line mental formula: green light at 550 nm is 2.25 eV, a 10 keV X-ray is 0.124 nm. Visible photons carry a couple of electron-volts, exactly the energy scale of chemical bonds, which is why light drives photosynthesis and fades paint. A 100 MHz FM photon carries 0.4 µeV — billions of them are needed to do anything, which is why radio is a wave phenomenon in practice and gamma rays behave like bullets.
Other media, other waves
Open More options to change the wave speed. Light in glass travels at about c ÷ 1.5: the frequency is fixed by the source, so the wavelength shrinks by 1.5 and the colour, which your eye judges by frequency, does not change. Set 343 m/s and the calculator works for sound in air — concert A at 440 Hz is a 78 cm wave — but photon energy no longer means anything and the band is reported as not applicable.
Common mistakes
- Using km/h or a rounded c. The error is small but the constants are exact, so there is no reason to.
- Forgetting the prefix on frequency: 2.4 GHz Wi-Fi, not 2.4 Hz. Both unit dropdowns exist to stop that.
- Confusing photon energy with beam power. A laser's watts is photons per second times this energy.
Frequently asked questions
▸How do I convert wavelength to frequency?
Divide the speed of light by the wavelength in meters: f = c ÷ λ. For 500 nm, f = 299,792,458 ÷ 5 × 10⁻⁷ = 6.0 × 10¹⁴ Hz (600 THz).
▸How is photon energy related to wavelength?
E = hc ÷ λ. Shorter wavelength means higher energy per photon. In practical units, E in eV ≈ 1239.84 ÷ λ in nm.
▸What are the wavelengths of visible light?
Roughly 380 nm (violet) to 750 nm (red): violet 380–450, blue 450–495, green 495–570, yellow 570–590, orange 590–620, red 620–750 nm. The edges are conventional, and individual eyes differ.
▸Does wavelength change when light enters water or glass?
Yes — the speed drops to c ÷ n and the wavelength shrinks by the same factor, but the frequency and photon energy stay the same. Colour is set by frequency, so objects don't change colour under water.
▸Can I use this for sound?
Yes. Set the wave speed to 343 m/s (air at 20 °C) or about 1,480 m/s (water). Wavelength and frequency follow the same v = fλ; photon energy and spectrum bands only apply to electromagnetic waves.
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