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v = f × λ

Wavelength and frequency calculator

Enter any two of speed, frequency and wavelength. The page solves the third, and for light it also gives the energy of one photon.

Short answer: green light at 550 nm in vacuum has a frequency of5.45 × 10¹⁴ Hz and each photon carries about 3.61 × 10⁻¹⁹ J. Sound at 343 m/s with a 0.68 m wavelength is 504 Hz.

One equation, every wave

Light, sound, water and radio all obey v = fλ. Fix the speed and frequency and wavelength trade off, which is why an FM station’s wavelength is metres while a mobile phone’s is centimetres — and why tuning a radio is really choosing a wavelength.

Worked example

A 100 MHz FM signal: λ = 299,792,458 ÷ 100,000,000 = 3.0 m. A 2.4 GHz Wi-Fi signal: 12.5 cm. The shorter antenna on your phone is not a design choice so much as arithmetic.

Wave questions

What is the wave equation?

v = fλ — speed equals frequency times wavelength. Light travels at 299,792,458 m/s in vacuum and sound at about 343 m/s in air at 20 °C, so the same wavelength means very different frequencies.

How do I find the frequency of a colour of light?

Enter 299792458 for the speed and the wavelength in metres: green light at 550 nm (5.5 × 10⁻⁷ m) is 5.45 × 10¹⁴ Hz. The page reports the frequency cleanly, without a trailing 0.5 from binary rounding.

What is the photon energy for?

E = hf with Planck’s constant, given for electromagnetic waves only. It explains why ultraviolet damages skin while radio does not: 5.45 × 10¹⁴ Hz carries about 3.6 × 10⁻¹⁹ J per photon, radio photons carry a millionth of that.

Does the speed of sound change the answer?

Yes — sound is faster in warm air, water and steel. Enter the speed for your medium rather than assuming 343 m/s, or the wavelength will be wrong by the same proportion.

Related tools

Unit converterLengths from nanometres to kilometres.Kinetic and potential energy calculatorEnergy in joules and kilocalories.Scientific notation converterVery large and very small numbers.