The half-wave dipole is the simplest useful antenna in radio, and it is the reference every other antenna is judged against. Two wires, fed in the middle, each one quarter wavelength long, give a predictable antenna for any band. The problem is the arithmetic: wavelength changes with frequency, so every band needs a different length. This dipole antenna length calculator does that arithmetic for you, in feet and metres, from the classic 468 formula that amateurs have used for generations.
The formula is easy to state. Total dipole length in feet equals 468 divided by frequency in megahertz. Each leg is half of that, so 234 divided by frequency. For example, at 14.2 megahertz, in the 20 metre amateur band, the total is 468 divided by 14.2, about 33 feet, or about 10 metres, with each leg near 16.5 feet. At 7.1 megahertz the total is about 66 feet, and at 28.5 megahertz it is about 16.4 feet. The tool gives both feet and metres because wire is sold in both systems.
Where does 468 come from? A free-space half wavelength in feet is about 492 divided by frequency, from the speed of light. But a real wire antenna is shorter than free space predicts, because radio waves travel slightly slower in wire than in space and because the wire ends have capacitance. The factor 468 builds in that shortening, roughly 5 percent, and it matches measured dipoles well for thin wire at ordinary heights. Thicker wire, nearby metal, and low height all shift resonance a little, which is why the formula is a starting point, not a final answer.
Height and surroundings matter as much as length. A dipole high and clear, at least half a wavelength above ground, behaves close to theory and radiates well at low angles for long distance. The same dipole low over a roof or near gutters and metal will resonate at a different frequency and lose energy to nearby objects. If your first cut does not match the formula, height and surroundings are the first suspects, not the formula itself. Move the antenna or raise it before you cut wire away.
Build practice is simple and forgiving if you cut long. Cut each leg a few percent longer than the calculator says, hang the antenna, and measure with an antenna analyzer or a standing wave meter. Trim equal small amounts from both legs and remeasure until the lowest standing wave ratio sits on your chosen frequency. Never cut both legs at once by large steps, and never trust a single meter reading taken near metal or at ground level. Patience here is what separates a working antenna from a disappointing one.
Feeding the dipole deserves a short note. The centre feed point of a half-wave dipole in free space is near 73 ohms, which suits 50 ohm coaxial cable through a balun reasonably well, with a standing wave ratio near 1.5. A balun, a short device that converts balanced antenna to unbalanced cable, keeps current off the outside of the cable and keeps the pattern clean. Without one, the cable itself can radiate and pick up noise. For receiving only, these details matter far less, and almost any wire length will hear signals.
Safety and law come before performance. Never raise an antenna near power lines, because contact can kill, and keep the antenna clear of places where people can touch it while you transmit. Transmitting requires a licence in most countries, and each licence carries band, power, and antenna rules. This calculator is an educational estimator: it teaches the formula and gives a build starting point. Real transmitting antennas need proper measurement with an analyzer and must follow your local regulations.
In short, this tool turns a frequency into a dipole length you can cut: total feet from 468 divided by frequency, each leg from 234 divided by frequency, both also in metres. Cut long, raise the antenna clear, trim in small equal steps while measuring, and check your licence rules. The dipole is simple, cheap, and honest, and it remains the antenna every beginner should build first.