About this calculator
Enter a frequency (radio, Wi-Fi, light) to find its wavelength, or a wavelength to find the frequency. The calculator also gives the energy of one photon in joules and electronvolts.
It uses the speed of light in a vacuum, 299,792,458 m/s.
Worked examples
Real numbers, worked out by the same calculator. Press “Use these numbers” to try one above.
A 100 MHz FM radio signal
- Wavelength
- 2.99792 m
- Frequency
- 100 MHz
- Photon energy
- 6.6261 × 10^-26 J (4.1357e-7 eV)
A wave of frequency 100 MHz has a wavelength of 2.99792 m in a vacuum, and each photon carries 4.1357e-7 eV.
Show the working
- Wave speed = frequency × wavelength, and light travels at c = 299,792,458 m/s in a vacuum.
- Wavelength = c ÷ frequency = 299,792,458 ÷ 1 × 10^8 = 2.9979 × 10^0 m.
- Photon energy E = h × frequency = 6.62607015 × 10^-34 × 1 × 10^8 = 6.6261 × 10^-26 J, which is 4.1357e-7 eV.
Green light at 550 nm
- Frequency
- 545.077 THz
- Wavelength
- 550 nm
- Photon energy
- 3.6117 × 10^-19 J (2.25426 eV)
A wave of frequency 545.077 THz has a wavelength of 550 nm in a vacuum, and each photon carries 2.25426 eV.
Show the working
- Wave speed = frequency × wavelength, and light travels at c = 299,792,458 m/s in a vacuum.
- Wavelength = c ÷ frequency = 299,792,458 ÷ 5.4508 × 10^14 = 5.5 × 10^-7 m.
- Photon energy E = h × frequency = 6.62607015 × 10^-34 × 5.4508 × 10^14 = 3.6117 × 10^-19 J, which is 2.25426 eV.
2.4 GHz Wi-Fi
- Wavelength
- 124.914 mm
- Frequency
- 2.4 GHz
- Photon energy
- 1.5903 × 10^-24 J (9.9256e-6 eV)
A wave of frequency 2.4 GHz has a wavelength of 124.914 mm in a vacuum, and each photon carries 9.9256e-6 eV.
Show the working
- Wave speed = frequency × wavelength, and light travels at c = 299,792,458 m/s in a vacuum.
- Wavelength = c ÷ frequency = 299,792,458 ÷ 2.4 × 10^9 = 1.2491 × 10^-1 m.
- Photon energy E = h × frequency = 6.62607015 × 10^-34 × 2.4 × 10^9 = 1.5903 × 10^-24 J, which is 9.9256e-6 eV.
The wave equation
For any wave, speed = frequency × wavelength. For light and radio waves in a vacuum the speed is c = 299,792,458 m/s, so wavelength = c ÷ frequency and frequency = c ÷ wavelength. Higher frequency means shorter wavelength.
Photon energy
Each photon of light carries energy E = h × f, where h is Planck's constant, 6.62607015 × 10⁻³⁴ J·s. One electronvolt is 1.602176634 × 10⁻¹⁹ J. Green light at 550 nm carries about 2.25 eV per photon; X-rays carry thousands of times more.
Typical values
| Wave | Frequency | Wavelength |
|---|---|---|
| FM radio | 100 MHz | 3 m |
| Wi-Fi | 2.4 GHz | 12.5 cm |
| Red light | ≈ 430 THz | ≈ 700 nm |
| Violet light | ≈ 750 THz | ≈ 400 nm |
Frequently asked questions
How do I convert frequency to wavelength?
Divide the speed of light (299,792,458 m/s) by the frequency in hertz.
What is the wavelength of 2.4 GHz?
About 12.5 cm.
How much energy does a photon carry?
E = h × f: Planck's constant times the frequency.
Does it work for sound?
No. Sound travels at about 343 m/s in air, far slower than light. This calculator uses the speed of light.
Formulas tested against hand-worked answers. Last reviewed 29 September 2026. These calculators do arithmetic only; they are not financial, tax or legal advice.