Wavelength to frequency converter
Enter a wavelength or a frequency, pick the medium, and get the other one. The speed in vacuum is the exact speed of light; for water, glass or sound in air, enter your own wave speed.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Type a number and choose whether it is a wavelength or a frequency.
- Leave the wave speed on vacuum, or choose custom and enter a speed in m/s.
- Read the wavelength, frequency, period and photon energy.
| Quantity |
Formula |
| Wavelength |
λ = v / f |
| Frequency |
f = v / λ |
| Period |
T = 1 / f |
| Photon energy |
E = h f |
Worked example
Green light of 500 nm in vacuum has a frequency of 299,792,458 ÷ 5 × 10⁻⁷ ≈ 5.9958 × 10¹⁴ Hz (about 599.6 THz). Its photon energy is 6.62607015 × 10⁻³⁴ × 5.9958 × 10¹⁴ ≈ 3.973 × 10⁻¹⁹ J, which is about 2.480 eV.
Tips
- An FM station at 100 MHz has a wavelength of about 3 m in air.
- Radio waves in air travel at almost exactly the vacuum speed; the difference is under 0.03%.
- Visible light spans roughly 380 to 750 nm.
Frequently asked questions
What is the formula for wavelength and frequency?
λ = v / f, where λ is the wavelength, f the frequency and v the speed of the wave in the medium. In vacuum v is the speed of light, c = 299,792,458 m/s exactly.
Does the frequency change when a wave enters another medium?
No. The frequency stays the same, and the speed and wavelength change together. Light in glass has a shorter wavelength than in vacuum, but the same frequency. Enter the speed in the medium as a custom speed to get the wavelength there.
How is the photon energy calculated?
E = h × f with the Planck constant h = 6.62607015 × 10⁻³⁴ J·s (exact). The result is also shown in electronvolts, using 1 eV = 1.602176634 × 10⁻¹⁹ J. Photon energy depends only on the frequency, not on the medium. It applies to light and other photons, not to sound.
Can I use it for sound?
Yes for the wavelength and frequency part: choose custom speed and enter about 343 m/s for air at 20 °C. Ignore the photon energy rows, which only make sense for electromagnetic waves.