Wavelength to Frequency Calculator
Convert the wavelength of light or radio waves to frequency with f = c ÷ λ. Enter the wavelength in m, cm, mm, µm or nm and read the frequency in Hz, kHz, MHz, GHz or THz.
Last updated: September 2026
Frequency
99.93 MHz
Formula below · 3 sources (physics.nist.gov, science.nasa.gov, hyperphysics.phy-astr.gsu.edu) · Updated Sep 2026
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About this calculator
Every electromagnetic wave, from radio to visible light to X-rays, travels through a vacuum at the speed of light, c = 299,792,458 m/s (an exact, defined value). Wavelength λ and frequency f are tied together by c = f × λ, so:
f = c ÷ λ
With the defaults, a 3 m wavelength gives 299,792,458 ÷ 3 = 99,930,819 Hz, which is 99.93 MHz, inside the 88–108 MHz FM broadcast band.
Units
Pick the unit your wavelength is given in; the calculator converts it to metres first (1 nm = 10⁻⁹ m, 1 µm = 10⁻⁶ m). Choose the output unit that suits the wave: MHz or GHz for radio and microwaves, THz for infrared and visible light. Green light at 550 nm is 545.08 THz (5.451 × 10¹⁴ Hz). The tile under the result always shows the frequency in plain hertz.
Limits
The formula uses the vacuum speed of light, which is also accurate to about 0.03% in air. Inside glass, water or a cable the wave slows to c ÷ n (n is the refractive index): the frequency stays the same and the wavelength shrinks, so enter the vacuum (free-space) wavelength. Sound is not an electromagnetic wave; it travels at about 343 m/s in air and needs a different wave speed.
| Wave | Wavelength | Frequency |
|---|---|---|
| FM radio | 3 m | 99.93 MHz |
| Hydrogen line (radio astronomy) | 21.1 cm | 1,420.4 MHz |
| Wi-Fi 2.4 GHz band | 12.5 cm | 2.398 GHz |
| Telecom fibre laser | 1550 nm | 193.41 THz |
| Red light | 700 nm | 428.27 THz |
| Green light | 550 nm | 545.08 THz |
| Violet light | 400 nm | 749.48 THz |
| X-ray | 0.1 nm | 2.998 × 10¹⁸ Hz |
How to use
Enter the wavelength, choose its unit, and choose the unit you want the frequency in. Example 1 (FM radio): 3 m, shown in MHz. 299,792,458 ÷ 3 = 99,930,819 Hz = 99.93 MHz. Example 2 (green light): 550 nm, shown in THz. 299,792,458 ÷ 0.00000055 = 5.451 × 10¹⁴ Hz = 545.08 THz. Example 3 (Wi-Fi): 12.5 cm, shown in GHz. 299,792,458 ÷ 0.125 = 2,398,339,664 Hz = 2.4 GHz.
Frequently asked questions
What is the formula to convert wavelength to frequency?
Frequency equals the speed of light divided by the wavelength: f = c ÷ λ, with c = 299,792,458 m/s and λ in metres. A 2 m wavelength is 299,792,458 ÷ 2 = 149,896,229 Hz, about 149.9 MHz.
How do I convert nanometres to frequency?
Multiply the nanometres by 10⁻⁹ to get metres, then divide c by it, or select nm as the unit here. 700 nm red light: 299,792,458 ÷ 0.0000007 = 4.283 × 10¹⁴ Hz = 428.27 THz.
Why does a shorter wavelength mean a higher frequency?
The wave speed is fixed, so frequency × wavelength must stay equal to c. Halve the wavelength and twice as many crests pass each second, doubling the frequency.
Does this work for sound waves?
No. Sound travels at about 343 m/s in air at 20 °C, not at the speed of light, so f = 343 ÷ λ for sound. This calculator is for light, radio and other electromagnetic waves.
What about light inside glass or fibre?
In a material the wave slows to c ÷ n and the wavelength shortens by the same factor, while the frequency does not change. Enter the free-space wavelength (the one quoted for lasers and radio channels) to get the correct frequency.
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Sources & references
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