Wavelength Calculator
Wavelength from frequency, or frequency from wavelength, for light and radio at the speed of light or any wave at a speed you enter, with the photon energy.
Result
Wavelength: 2.998 m
Light is taken at its exact speed in a vacuum. In air it is very slightly slower, and in glass or water much slower.
- Frequency
- 100 MHz
- Wave speed
- 983,571,056 ft/s (299,792,458 m/s)
- Period, one cycle
- 1 × 10^−8 s
- Photon energy
- 4.13567 × 10^−7 eV
- Photon energy in joules
- 6.62607 × 10^−26 J
https://calcgallery.com/physics/wavelength-calculator/
Results come from the published equations applied to the values you enter. They are not electrical design, conductor sizing, laboratory safety or medical guidance. Weather indices describe a standard person in standard conditions and are not a forecast. Where codes apply, local rules vary and must be checked. Read the full disclaimer
How to use the Wavelength Calculator
- Choose whether to find the wavelength, the frequency or the wave’s speed.
- For light, radio, microwaves or X-rays, leave the wave as light in a vacuum. For sound or any other wave, choose another wave and enter its speed.
- Enter the frequency or the wavelength and read the other, with the period and, for light, the energy of one photon.
The formulas
v = f × λλ = v ÷ f, f = v ÷ λperiod T = 1 ÷ ffor light v = c = 299,792,458 m/sphoton E = h × f = h × c ÷ λ, h = 6.62607015 × 10⁻³⁴ J·sThe speed of light and Planck’s constant are exact values fixed by the SI. The photon energy is also shown in electronvolts, the usual unit for a single photon.
Limits
The page assumes a steady wave travelling at one speed. It does not work out the speed of sound or of light in a material for you: enter it. Photon energy is only meaningful for electromagnetic waves, so it is left blank for any other wave.
With your numbers
- v = f × λ, with v = c = 299,792,458 m/s, f = 1 × 10^8 Hz and λ = 2.99792 m
Quick reference
Light is taken at its exact speed in a vacuum. In air it is very slightly slower, and in glass or water much slower.
| Example | Result |
|---|---|
| FM radio, 100 MHz | Wavelength: 2.998 m |
| Wi-Fi, 2.4 GHz | Wavelength: 12.49 cm |
| Violet light, 430 nm | Frequency: 697.2 THz |
| Green laser, 532 nm | Frequency: 563.5 THz |
| Concert A, 440 Hz, in air at 343 m/s | Wavelength: 77.95 cm |
| String wave, 2.5 m at 2 Hz | Wave speed: 5 m/s |
Where the numbers come from
The fixed figures this calculator relies on, and the published source each one was checked against. How the calculators are built and checked
2 sources
SI Brochure, 9th ed. (BIPM, 2019), section 2.2, Table 1, the seven defining constants: "speed of light in vacuum c 299 792 458 m s−1", https://www.bipm.org/documents/20126/41483022/SI-Brochure-9-EN.pdf
Used for
- Speed of light in vacuum, c, exact by the definition of the metre.
SI Brochure, 9th ed. (BIPM, 2019), section 2.2, Table 1, the seven defining constants: "Planck constant h 6.626 070 15 × 10−34 J s", https://www.bipm.org/documents/20126/41483022/SI-Brochure-9-EN.pdf
Used for
- Planck constant, h, exact since the 2019 redefinition of the SI.
Common questions about the Wavelength Calculator
- How do I convert frequency to wavelength?
- Divide the wave’s speed by its frequency: λ = v ÷ f. Radio travels at the speed of light, 299,792,458 m/s, so a 100 MHz FM station has a wavelength of just under 3 m, and 2.4 GHz Wi-Fi about 12.5 cm.
- How do I convert wavelength to frequency?
- f = v ÷ λ. Violet light of 430 nm has a frequency of about 697 THz, 697 million million cycles a second. Frequency and wavelength move opposite ways: halve the wavelength and the frequency doubles.
- How do I find the energy of a photon?
- E = hf, Planck’s constant times the frequency, or hc ÷ λ from the wavelength. A 430 nm photon carries about 2.88 eV, 4.62 × 10⁻¹⁹ J, as in OpenStax University Physics Volume 3, example 6.7. Higher frequency means more energy per photon, which is why ultraviolet burns and radio does not.
- Does this work for sound?
- Yes, choose another wave and enter the speed of sound for the medium. In air at 20 °C, OpenStax gives 343 m/s, so concert A at 440 Hz has a wavelength of about 78 cm. In water sound travels over four times faster and its wavelengths are longer to match. Photon energy does not apply to sound.
- Why is the speed of light fixed here?
- Since 1983 the metre has been defined by the speed of light, which is therefore exactly 299,792,458 m/s in a vacuum. In air light is very slightly slower, and in glass or water noticeably so; for those, choose another wave and enter the speed there.