Electronics / Radio
Frequency to Wavelength Calculator (with Antenna Length)
Convert a radio frequency to its wavelength or a wavelength to its frequency, in air or in cable with a velocity factor, and get the length of a half-wave dipole and a quarter-wave antenna.
Frequency to Wavelength Calculator (with Antenna Length): Radio waves travel at the speed of light, 299,792,458 m/s, so wavelength = speed ÷ frequency: 100 MHz has a wavelength of 3.00 m, and 2.4 GHz of 12.5 cm. In cable they travel slower, by the cable's velocity factor. A half-wave dipole is cut to about 95% of half the free-space wavelength, and a quarter-wave antenna to about 95% of a quarter, to allow for the end effect. Runs 100% locally in your browser with zero server file uploads.
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Wavelength = speed ÷ frequency, with radio waves travelling at the speed of light, 299,792,458 m/s, in air. In cable they are slower, by the velocity factor printed in the cable's specification. Wire antennas are cut about 5% shorter than the free-space half or quarter wave because of the end effect; trim to tune.
Worked examples
FM radio at 100 MHz: wavelength 3.00 m, half-wave dipole about 1.42 m, quarter wave about 71 cm. The 2 m amateur band at 145 MHz: wavelength 2.07 m, quarter wave about 49 cm.
For signal levels along a radio link, use the decibel calculator.
Sound instead of radio
The same formula works for sound with the speed of sound, about 343 m/s in air at 20 °C: a 343 Hz tone has a 1 m wavelength. Enter the velocity factor as 343 ÷ 299,792,458 to use this tool, or simply divide 343 by the frequency.
Light uses it too: green light at about 545 THz has a wavelength of about 550 nm.
How to use it
- Choose frequency to wavelength, or the other way.
- Enter the frequency with its unit, or the wavelength in metres, and the velocity factor (1 in air).
- Read the result and the antenna lengths.
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Related tools
Frequently asked questions
What is the wavelength of Wi-Fi?
About 12.5 cm at 2.4 GHz and about 5.8 cm at 5.2 GHz.
What is a velocity factor?
How fast a signal travels in a cable compared with free space: about 0.66 for solid polyethylene coax and 0.8 or more for foam types. It matters when cutting cable to a fraction of a wavelength.
Why is the antenna shorter than half a wavelength?
The thickness of the wire and the effect at its ends make it resonate slightly lower, so it is cut about 5% short and trimmed to tune.
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