Antenna Calculator: Dipole, ¼-Wave & 5/8-Wave

Need to know how long your antenna should be? Our antenna length calculator converts your operating frequency into wavelength and practical starting dimensions for quarter-wave, half-wave, dipole, and 5/8-wave antennas. Results are provided in both metric and imperial units, making it easy to plan an antenna for ham radio, SDR, scanners, or other radio applications.

Enter your frequency below to get started, then use the calculated dimensions as a starting point for building and tuning your antenna.

Radio & Antenna Calculator

Calculate wavelength and practical starting dimensions for quarter-wave, half-wave, dipole, and 5/8-wave antennas.

Frequency

Frequency unit

Common ham-band presets

Practical correction factor

Calculated dimensions

Full wavelength—

Quarter-wave—

Half-wave element—

Half-wave dipole—

Dipole each leg—

5/8-wave vertical—

Practical half-wave dipole formula

For a commonly used amateur-radio starting point, a half-wave dipole is approximately 468 ÷ frequency in MHz = total length in feet. This empirical formula is shown separately from the free-space wavelength calculation because the two methods use different practical assumptions.

468 ÷ MHz dipole—

468-formula each leg—

Before you cut wire

These calculations provide starting dimensions rather than guaranteed final resonant lengths. Conductor diameter, end effects, mounting height, nearby objects, insulation, ground conditions, and the surrounding environment can all affect resonance. Build the antenna slightly long when practical, then trim and check it with an SWR meter or antenna analyzer.

Calculate Your Coax Cable Loss

How much RF power is being lost between your radio and antenna? Use our Coax Cable Loss Calculator to estimate attenuation based on cable type, frequency, and cable length—and see how much power actually reaches your antenna.

👉 Calculate Your Coax Cable Loss →