RF Wavelength & Antenna Calculator
Convert frequency to wavelength and estimate full, half and quarter-wave antenna lengths.
RF Wavelength & Antenna Calculator
How to use the RF Wavelength & Antenna Calculator
Enter the operating frequency, then choose a practical material estimate or enter a manufacturer-specified factor. The adjusted full, half and quarter-wave lengths update automatically.
How it works
Wavelength is the speed of propagation divided by frequency. In free space the factor is 1.00. Insulating material around a conductor slows the wave, so a cable with a velocity factor of 0.66 has an electrical wavelength only about 66% as long as the equivalent free-space wavelength. Antenna elements are also commonly shortened from the theoretical value because of end effects and their construction.
Example: At 433.92 MHz, the free-space wavelength is roughly 0.691 m and a theoretical quarter wavelength is about 17.3 cm. Applying a 0.95 wire-antenna estimate gives approximately 16.4 cm. A solid-polyethylene coaxial stub using 0.66 would be approximately 11.4 cm, although its manufacturer’s specification should be preferred.
What to keep in mind
The presets are realistic starting estimates, not universal specifications. Coax types with the same general name can use different dielectric materials and velocity factors. For cable stubs and phasing lines, use the cable data sheet. For an antenna, cut slightly long and trim while measuring resonance; element diameter, insulation, ground plane, bends and nearby objects can all change the final length.
Frequently asked questions
What velocity factor should I use?
Use 1.00 for a theoretical free-space wavelength, about 0.95 as a first estimate for many bare-wire antennas, or the cable manufacturer’s specified value for coaxial stubs and feed-line calculations.
Are the coax presets exact?
No. They represent common constructions: solid polyethylene is often near 0.66, PTFE near 0.70, and foam polyethylene commonly around 0.78 to 0.85. Always check the exact cable data sheet when length matters.
Why might the finished antenna need trimming?
Physical construction and surroundings change its electrical length, so practical tuning is normally required.
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