Dipole Antenna Calculator

The classic formula is: Total Length (ft) = 468 / Frequency (MHz). This accounts for a velocity factor of approximately 0.95 for typical bare copper wire. For metric, the formula is Total Length (m) = 142.65 / Frequency (MHz). The antenna is cut to resonate at your chosen frequency, meaning its electrical length equals one half wavelength.

Larger diameter wire (lower AWG number, e.g. 12 AWG) lowers the Q of the antenna, which broadens its bandwidth — meaning it will perform acceptably over a wider range of frequencies. Thinner wire (e.g. 16 AWG) is lighter and cheaper but has a narrower bandwidth and slightly higher resistive losses. For most amateur radio use, 14 AWG is a good compromise.

A Balun (Balanced-to-Unbalanced transformer) is placed at the feedpoint of the dipole where the coax connects. A dipole is a balanced antenna, while coaxial cable is an unbalanced feedline. A 1:1 Balun prevents stray RF currents from flowing back down the coax shield, which can cause interference, distorted radiation patterns, and RF in the shack. It is strongly recommended for any coax-fed dipole.

A resonant half-wave dipole in free space has a feedpoint impedance of approximately 73 ohms. Both 50-ohm and 75-ohm coaxial cable work well with a dipole — the SWR with 75-ohm coax will be slightly lower at resonance. Using a 1:1 Balun at the feedpoint and ensuring the antenna is cut for the correct frequency will minimize SWR across either coax type.

A horizontal dipole radiates strongest broadside (perpendicular) to the wire, with nulls off the ends. For local and regional contacts, a horizontal dipole at least half a wavelength above ground provides good low-angle radiation. Orienting the dipole broadside toward your target area maximizes signal in that direction. An inverted-V configuration (center elevated, ends closer to ground) is a popular compromise when a single high support point is available.

Velocity factor (VF) is the ratio of the speed of an electromagnetic wave traveling through a material compared to the speed of light in a vacuum. For bare copper wire in free space, VF is approximately 0.95–0.97, which is why the constant 468 (rather than 492) is used in the standard formula. Antennas made from insulated wire or inside tubing may require a lower velocity factor, resulting in a physically shorter antenna than the free-space calculation predicts.

Yes — the half-wave dipole formula applies to any frequency. This calculator works for shortwave listening antennas, CB (27 MHz), FM broadcast (88–108 MHz), emergency communications, and experimental use. Simply enter the desired center frequency in MHz and the calculator returns all required lengths. Always check local regulations before transmitting on any frequency.

The calculated length is a very good starting point, but real-world factors mean you should cut the antenna slightly long (2–5%) and trim to resonance using an antenna analyzer or SWR meter. Factors that shift resonance include height above ground, proximity to structures or trees, wire insulation, end effects, and the exact velocity factor of your wire. Always measure and trim rather than cutting to the exact calculated length.