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Antenna Length Calculator
Estimate a free-space half-wave dipole or quarter-wave monopole from frequency. Adjust the shortening factor to see a practical starting length and each dipole leg.
How do I calculate dipole antenna length from frequency?
First calculate wavelength as the speed of light divided by frequency. A half-wave dipole is about half that wavelength in total, with two equal legs; a quarter-wave monopole is about one quarter. An editable shortening factor can provide a practical starting estimate, but the final length depends on antenna design and surroundings.
Frequently asked questions
How do I calculate dipole antenna length from frequency?
First calculate wavelength as the speed of light divided by frequency. A half-wave dipole is about half that wavelength in total, with two equal legs; a quarter-wave monopole is about one quarter. An editable shortening factor can provide a practical starting estimate, but the final length depends on antenna design and surroundings.
Are my antenna values uploaded?
No. The calculation runs in this browser; your entered values are not uploaded or saved by this tool.
What is the length of a half-wave dipole at 100 MHz?
In free space, the wavelength at 100 MHz is about 2.998 m, so an ideal half-wave dipole is about 1.499 m total, or about 0.749 m per leg. A practical antenna may use a shortening factor and should be tuned in its installed environment.
How long is a quarter-wave antenna?
Its ideal free-space conductor length is one quarter of wavelength: speed of light divided by four times frequency. The actual tuned length can differ with the conductor, feed, ground and surroundings.
What does the shortening factor mean?
It multiplies the ideal free-space element length to provide a starting estimate for a practical conductor. The default is only a rule of thumb; it is not the coaxial cable velocity factor and does not replace measurement or tuning.
Does this calculator guarantee a tuned or safe antenna?
No. It estimates basic half-wave dipole or quarter-wave monopole geometry. Real impedance and resonance depend on construction and the site. Follow radio regulations and safe installation practices, and verify with suitable instruments.