Dipole Antenna Calculator

How to use

1. 1Choose an antenna type: half-wave dipole, folded dipole, quarter-wave vertical, 5/8-wave vertical, or full-wave loop.
2. 2Keep Frequency to length selected and enter your target frequency, choosing Hz, kHz, MHz, or GHz. A band preset fills in a common frequency in one click.
3. 3Set the velocity factor, or tap a preset: bare wire (0.95), thin wire (0.98), insulated wire (0.92), or free space (1.00).
4. 4Read the total wire length and, for a dipole, each leg, in metric and in feet and inches, then copy any value or copy all results.
5. 5To work backwards, switch to Length to frequency, enter the wire length in metres, centimetres, feet, or inches, and read the resonant frequency.

About this tool

Dipole Antenna Calculator turns a target frequency into the wire length you actually cut, for the resonant wire antennas amateur radio operators, shortwave listeners, and electronics hobbyists build most often. It starts from the exact relationship between frequency and wavelength, lambda = c / f with c set to 299,792,458 metres per second, then multiplies that wavelength by the fraction the antenna uses (one half for a center-fed dipole, one quarter for a quarter-wave vertical, a full wavelength for a loop, and 0.625 for a 5/8-wave vertical) and by a velocity, or shortening, factor that accounts for end effect on real wire. The result is shown several ways at once: the total wire length and, for a dipole, each leg, given in metres or centimetres and in feet and inches and decimal feet, so the number is ready whether you measure with a tape in feet or a metric rule. Because the math is exact rather than a single rule of thumb, the tool also prints the matching free-space wavelength and the classic handbook constants (468 divided by the frequency in megahertz for a dipole, 234 for each leg or a quarter-wave vertical, and 1005 for a full-wave loop) so you can sanity-check the figures against any antenna book. The velocity factor is adjustable with one-click presets for bare wire (about 0.95, which reproduces the 468 rule), thin wire or tubing (about 0.98, a good starting point for loops), insulated wire (about 0.92, which runs shorter), and free space (1.00) when you want the pure electromagnetic length. A reverse mode flips the calculation around: enter the length of an antenna you already have, in metres, centimetres, feet, or inches, and the tool reports the frequency it resonates on, which is handy for identifying a mystery wire or estimating where a cut antenna will tune. Quick band presets load common amateur and CB frequencies such as 40 metres, 20 metres, 27 MHz CB, and 2 metres so you can see a realistic answer immediately. These figures get you very close, but a real antenna also depends on its height above ground, nearby objects, wire diameter, and insulation, so the standard advice applies: cut the wire slightly long, raise the antenna, and trim a little at a time for the lowest SWR at your operating frequency. Everything runs in your browser, so the frequencies and lengths you type are never uploaded.

Free to use. Works in your browser. No signup, no login.