Wavelength ↔ Frequency
Convert between wavelength and frequency
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Wavelength ↔ Frequency helps you convert between wavelength and frequency — free, instant, in your browser. Drop Value into Wavelength ↔ Frequency — the figure refreshes as you type. Wavelength ↔ Frequency prints the result and its working. Students and professionals reach for Wavelength ↔ Frequency when speed matters. You can disconnect once Wavelength ↔ Frequency has loaded; the arithmetic runs locally. Wavelength ↔ Frequency handles wavelength frequency calculator speed of light the same way as free online wavelength ↔ frequency calculator — one of the Science tools on CalcProMaster. Wavelength ↔ Frequency is designed for real people. Labels stay plain. Wavelength ↔ Frequency stays bookmarked for next time.
What the defaults give
550 nm in vacuum is a frequency of 5.45 × 10¹⁴ Hz.
That is 545 terahertz — the middle of the visible spectrum, which is why 550 nm looks green.
The formula
f = v ÷ λ, and in the other direction λ = v ÷ f.
In vacuum v is about 299,792,458 m/s, so 299,792,458 ÷ 550 × 10⁻⁹ = 5.45 × 10¹⁴ Hz.
Worked examples
550 nm in vacuum → 5.45 × 10¹⁴ Hz (green light)
700 nm in vacuum → 4.28 × 10¹⁴ Hz (red light)
400 nm in vacuum → 7.49 × 10¹⁴ Hz (violet)
550 nm in glass (n = 1.5) → 3.63 × 10¹⁴ Hz at the same colour
1 m radio wave → 300 MHz
What changes in a medium
The frequency of light is set by the source and does not change when it enters glass or water. The speed drops — divided by the refractive index — and the wavelength shrinks with it, which is why a lens can bend light without changing its colour. The calculator uses the medium you select to get the speed right, so a wavelength quoted inside glass gives a different frequency than the same number in vacuum.
Where this is used
- Antennas. Size follows wavelength, so a 300 MHz signal needs an antenna around a metre.
- Spectroscopy. Wavelength identifies a substance; frequency places it on the electromagnetic spectrum.
- Fibre optics. Wavelength bands — 850, 1310, 1550 nm — set the loss and dispersion of a link.
- Sound and ultrasound. The same relation applies with the speed of sound in the medium, around 343 m/s in air.
Watch the units: nanometres for visible light, metres for radio, and hertz for frequency, so convert before dividing.
The conversion is the same in any medium, but the speed is not: 550 nm in vacuum gives 5.45 × 10¹⁴ Hz, and the same wave in glass travels about two-thirds as fast, so its wavelength shortens while the frequency stays fixed. That is why colour is a frequency and a wavelength only means something with the medium named. The period, about 1.8 femtoseconds here, is the time one cycle takes.
Frequently Asked Questions
What frequency is 550 nm?
About 5.45 × 10¹⁴ Hz in vacuum, which is 545 THz — green light in the middle of the visible spectrum.
Does frequency change when light enters glass?
No. Frequency is fixed by the source. Speed and wavelength both drop by the refractive index, so the colour stays the same.
Why is wavelength quoted in nanometres?
Because visible light spans roughly 380–750 nm, and nanometres keep the numbers in a readable range rather than using 10⁻⁷ metres.
What is the wavelength of a 300 MHz signal?
About one metre in vacuum, from 3 × 10⁸ divided by 3 × 10⁸ Hz.
How do I convert the other way?
Divide the speed by the frequency to get wavelength. The calculator does it directly when you switch the conversion direction.
Does this work for sound?
Yes, with the speed of sound in the medium instead of the speed of light — about 343 m/s in air at room temperature.
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