Wavelength and Frequency Calculator
Convert wavelength, frequency, period and photon energy for light, radio and sound. Shows the spectrum band, visible colour, ITU radio band and nearest musical note.
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About this toolWhat is the Wavelength and Frequency Calculator?
This wavelength and frequency calculator converts between the four ways of describing a wave: wavelength λ, frequency f, period T and, for light, photon energy E. Choose the wave and medium (light in vacuum, light in glass or water, sound in air at any temperature, sound in water or steel, or a custom speed), enter any one value, and the rest follow from v = f λ and E = h f.
For light the result names the part of the spectrum (gamma, X-ray, UV-A/B/C, visible, infrared, microwave, radio), shows the approximate colour of visible wavelengths and gives the ITU radio band such as VHF or UHF. For sound it says whether the frequency is audible and names the nearest musical note with its offset in cents.
Units run from picometres to kilometres, hertz to petahertz, femtoseconds to seconds and meV to MeV, so the same tool handles a 2.4 GHz Wi-Fi antenna, a 532 nm laser pointer, an 8 keV X-ray line and a 440 Hz tuning fork.
- Wavelength, frequency, period and photon energy
- Light in vacuum or any refractive index; sound in air, water, steel
- Spectrum region, UV-A/B/C and visible colour swatch
- ITU radio band names and nearest musical note
- Exact SI constants c and h, wide unit ranges
How to use the Wavelength and Frequency Calculator
- Pick the wave and medium. For light in a medium enter the refractive index; for sound in air enter the temperature.
- Choose which value you know: wavelength, frequency, period or photon energy (light only).
- Type the value and select its unit.
- Read the other quantities, the angular frequency and wavenumber, and the band, colour or musical note.
- Copy the result or share a link that keeps your inputs.
Worked examples
Green laser pointer
Input
Light in vacuum, wavelength 532 nm
Output
563.5 THz, 2.331 eV, 18,797 cm⁻¹; visible, green
E = 1239.84 ÷ 532 = 2.331 eV. The frequency stays 563.5 THz in any medium.
Wi-Fi antenna length
Input
Light in vacuum, frequency 2.4 GHz
Output
Wavelength 12.49 cm; ITU band 9, UHF
A quarter-wave antenna is about 3.1 cm before the velocity factor of the conductor is applied.
Concert A in a warm room
Input
Sound in air at 20 °C, 440 Hz
Output
Wavelength 78.0 cm; A4, in tune
The speed of sound is 343.2 m/s at 20 °C. At 30 °C it is 349.0 m/s and the wavelength grows to 79.3 cm.
Copper X-ray tube
Input
Photon energy 8.04 keV
Output
Wavelength 0.1542 nm (1.542 Å); X-rays
This is close to the Cu Kα line used in X-ray diffraction.
Background and insight
Every wave satisfies v = f λ: wave speed equals frequency times wavelength. For light in vacuum v is the speed of light, c = 299,792,458 m/s, an exact value since the metre was redefined in 1983. The period is the inverse of frequency, and the angular frequency ω = 2πf appears in most physics equations. Spectroscopists often quote the wavenumber 1/λ in cm⁻¹ because it is proportional to energy.
Light comes in photons of energy E = h f, where Planck's constant h = 6.62607015 × 10⁻³⁴ J·s, exact since the 2019 SI redefinition. In electronvolts, E (eV) = 1239.84 ÷ λ (nm). A 532 nm green photon carries 2.33 eV, enough to drive photochemistry; a 2.4 GHz microwave photon carries about 10 µeV, a hundred-thousandth as much, which is why microwaves heat but do not ionise.
In a material, light slows to c ÷ n, where n is the refractive index, and its wavelength shrinks by the same factor while its frequency stays the same. Colour follows frequency, so a green laser still looks green under water even though its wavelength there is 399 nm. Sound in air travels at √(γRT ÷ M), about 331.3 m/s at 0 °C and 343.2 m/s at 20 °C; in water it is about 1,482 m/s and in steel nearly 6,000 m/s.
Common use cases
Radio and antennas
Convert a channel frequency into a wavelength to size dipoles, quarter-wave whips and Yagi elements.
Optics and lasers
Turn a laser wavelength into photon energy and frequency, or find the wavelength in glass or water.
Chemistry and spectroscopy
Move between nm, cm⁻¹, eV and kJ/mol for absorption bands and photochemistry.
Acoustics and music
Find the wavelength of a tone for room modes or speaker placement, and the note nearest any frequency.
Tips and limitations
- Band edges such as "visible is 380 to 750 nm" are conventions; human sensitivity fades gradually at both ends.
- Photon energy only makes sense for electromagnetic waves, so that option is hidden for sound.
- For radio antennas, real elements are a few percent shorter than the free-space fraction of a wavelength because of the conductor's velocity factor and end effects.
- Sound speed also depends on humidity, slightly. The calculator uses dry air, which is within about 0.5% for normal room conditions.
- The colour swatch is an approximation: monochromatic light is more saturated than any screen can show.
Frequently asked questions
How do you convert wavelength to frequency?
Divide the wave speed by the wavelength: f = v ÷ λ. For light in vacuum, f = 299,792,458 ÷ λ. A 500 nm wavelength is 599.6 THz.
How do I convert eV to nm?
Use λ (nm) = 1239.84 ÷ E (eV), from E = hc ÷ λ. A 2 eV photon is 619.9 nm (orange-red) and a 1 eV photon is 1239.8 nm (infrared).
What is the wavelength of 2.4 GHz Wi-Fi?
About 12.5 cm (0.1249 m). The 5.8 GHz band is about 5.2 cm. Antennas for these bands are fractions of those lengths.
Does light change frequency in water?
No. The frequency stays the same, the speed drops to c ÷ n and the wavelength shrinks by n. In water (n = 1.333) a 532 nm laser has a wavelength of 399 nm but still looks green.
What is the speed of sound used for sound waves?
For air, √(γRT ÷ M) with γ = 1.4 and M = 28.96 g/mol, which gives 331.3 m/s at 0 °C and 343.2 m/s at 20 °C. Fresh water at 20 °C is 1,482 m/s.
What range of frequencies can humans hear?
Roughly 20 Hz to 20 kHz for young adults, with the upper limit falling with age. Below 20 Hz is infrasound and above 20 kHz is ultrasound.
What are the wavelength ranges of visible colours?
Approximately violet 380 to 450 nm, blue 450 to 495, green 495 to 570, yellow 570 to 590, orange 590 to 620 and red 620 to 750 nm. The boundaries vary between sources because colour perception is continuous.
Is there an in-depth guide to the Wavelength and Frequency Calculator?
Yes. “Wavelength, Frequency and Photon Energy: One Equation, Every Wave” covers the background, how it works, common pitfalls and worked examples. Read the full guide.
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