Wavelength Frequency Calculator
Convert frequency to wavelength or wavelength to frequency for light, radio waves or sound, solve for wave speed, and see the period, photon energy and where your wave sits on the spectrum. Runs entirely in your browser.
λ = v / f · f = v / λ · E = h f
Electromagnetic spectrum
How to use the Wavelength Frequency Calculator
- Choose what to solve for: Wavelength, Frequency or Wave speed.
- Pick the medium, e.g. light in vacuum for radio and light, or sound in air at 20 °C for audio.
- Enter the known value and its unit, such as 2.4 GHz or 532 nm.
- Read the result in the highlighted field and change its unit to convert, then check the period and photon energy.
- See the band on the spectrum bar and press Copy result to paste the answer.
The wave equation: λ = v / f
Every wave obeys v = f × λ: the speed equals the frequency (cycles per second, in hertz) times the wavelength (the distance between two crests). Rearranged, λ = v / f and f = v / λ. For light and radio in a vacuum the speed is exactly c = 299,792,458 m/s. In a material with refractive index n, light travels at c / n; sound has its own speed in each medium.
| Wave | Frequency | Speed used | Wavelength |
|---|---|---|---|
| AM radio | 1 MHz | c | ≈ 300 m |
| FM radio | 100 MHz | c | ≈ 3.00 m |
| Wi-Fi / microwave oven | 2.4–2.45 GHz | c | ≈ 12.2–12.5 cm |
| Green laser | 563.5 THz | c | 532 nm |
| Note A4 | 440 Hz | 343 m/s (air, 20 °C) | ≈ 0.780 m |
| Medical ultrasound | 5 MHz | 1,481 m/s (water) | ≈ 0.296 mm |
Speed of waves in common media
| Medium | Speed |
|---|---|
| Light in vacuum (exact, SI definition) | 299,792,458 m/s |
| Light in air (n ≈ 1.000293) | ≈ 299,705,000 m/s |
| Light in water (n ≈ 1.333) | ≈ 224,900,000 m/s |
| Light in typical glass (n ≈ 1.5) | ≈ 199,900,000 m/s |
| Sound in dry air at 20 °C | ≈ 343 m/s |
| Sound in fresh water at 20 °C | ≈ 1,481 m/s |
| Sound in steel (longitudinal) | ≈ 5,960 m/s |
The speed of sound in air rises by roughly 0.6 m/s for every degree Celsius, so pick the custom speed option for other temperatures or materials.
Photon energy and the spectrum
For electromagnetic waves each photon carries E = hf, with Planck's constant h = 6.62607015 × 10⁻³⁴ J·s. A handy shortcut is E (eV) ≈ 1239.84 / λ (nm): red light at 650 nm is about 1.91 eV, violet at 400 nm about 3.10 eV, which is why ultraviolet and X-ray photons can break chemical bonds while radio photons cannot. The band boundaries shown by the tool are common conventions: radio (above 1 m), microwave (1 mm – 1 m), infrared (750 nm – 1 mm), visible (380 – 750 nm), ultraviolet (10 – 380 nm), X-ray (10 pm – 10 nm) and gamma (below 10 pm). Radio frequencies are also labelled with their ITU band, from ELF to EHF.
Frequently asked questions
How do you convert frequency to wavelength?
Divide the wave speed by the frequency: λ = v / f. For radio and light in a vacuum v = c = 299,792,458 m/s, so 100 MHz has a wavelength of 299,792,458 / 100,000,000 ≈ 3.00 m and 2.4 GHz Wi-Fi has about 12.5 cm.
How do you convert wavelength to frequency?
Divide the wave speed by the wavelength: f = v / λ. Green laser light at 532 nm has f = 299,792,458 / 532 × 10⁻⁹ ≈ 563.5 THz.
What is the wavelength of sound?
Use the speed of sound in the medium. In air at 20 °C sound travels at about 343 m/s, so the note A4 (440 Hz) has λ = 343 / 440 ≈ 0.78 m. In water (≈1,481 m/s) the same frequency has a wavelength of about 3.37 m.
How do I calculate photon energy?
E = hf, where h = 6.62607015 × 10⁻³⁴ J·s is Planck's constant. In electronvolts, E (eV) ≈ 1239.84 / λ (nm). A 532 nm green photon carries about 2.33 eV; a 0.1 nm X-ray photon about 12.4 keV.
Does the frequency change when light enters water or glass?
No. The frequency stays the same, but the speed drops to c / n and the wavelength shrinks by the same factor n (the refractive index). That is why the calculator uses the vacuum wavelength to name the spectrum band.
What is the relationship between period and frequency?
The period is the time for one full cycle: T = 1 / f. A 50 Hz mains supply has a period of 20 ms; a 1 GHz signal has a period of 1 ns.
Where are the boundaries between spectrum bands?
Band edges are conventions, not sharp physical limits. This tool uses: radio above 1 m, microwaves 1 mm to 1 m, infrared 750 nm to 1 mm, visible light 380 to 750 nm, ultraviolet 10 to 380 nm, X-rays 10 pm to 10 nm and gamma rays below 10 pm.