Dipole Antenna Calculator
Enter your target frequency to calculate antenna lengths for a half-wave dipole, quarter-wave vertical, and full-wave loop. Toggle between imperial and metric units.
The 468/f Formula Explained
The standard formula for a half-wave dipole antenna in feet is 468 / f(MHz). This number comes from dividing the speed of light (983.6 million feet/second) by two for a half wavelength, giving 491.8, then applying a ~5% correction factor for the end effect. The end effect occurs because current doesn't simply stop at the tips of a real antenna. It interacts with the wire's diameter and surrounding environment, making the antenna electrically longer than its physical length.
The metric equivalent is 142.65 / f(MHz) in meters. Both formulas give the total dipole length. Each leg is half that value. For a quarter-wave vertical, use 234 / f(MHz) feet or 71.325 / f(MHz) meters. For a full-wave loop, 1005 / f(MHz) feet or 306.27 / f(MHz) meters.
Three Antenna Types Compared
The half-wave dipole is the simplest and most common wire antenna. It consists of two equal-length elements connected to a feed line at the center. It has about 2.15 dBi of gain and a figure-eight radiation pattern, meaning it radiates best broadside to the wire. An ideal first antenna project.
The quarter-wave vertical uses a single radiating element with a ground plane (typically three or four radial wires). Its main advantage is omnidirectional coverage: it radiates equally in all horizontal directions, making it popular for repeater access and mobile operation.
The full-wave loop uses more wire but offers lower noise pickup and about 1 dB more gain than a dipole. It can be strung as a square, triangle, or diamond. Popular for HF operation where the extra wire length is manageable and the noise advantage matters.
Practical Tips for Cutting Antenna Wire
Always cut your wire 2–3% longer than the calculated length. Wire gauge, insulation, height above ground, and nearby objects all shift the resonant frequency slightly. By starting long, you can trim small amounts from each end and check your SWR after each trim until you hit the target frequency.
For wire gauge, 14 AWG stranded copper works well for most HF dipoles. It's strong enough to support its own weight over reasonable spans and easy to solder. For VHF/UHF antennas, solid copper or brass rod is more common since the elements are short enough that rigidity matters more than flexibility.
Common Ham Band Antenna Lengths
Pre-calculated half-wave dipole lengths for popular amateur radio bands, using the center frequency of each allocation:
| Band | Center Freq | Dipole (ft) | Dipole (m) |
|---|---|---|---|
| 40m | 7.15 MHz | 65.5 | 19.95 |
| 20m | 14.175 MHz | 33.0 | 10.06 |
| 15m | 21.225 MHz | 22.1 | 6.72 |
| 10m | 28.85 MHz | 16.2 | 4.94 |
| 6m | 52.0 MHz | 9.0 | 2.74 |
| 2m | 146.0 MHz | 3.2 | 0.98 |
| 70cm | 435.0 MHz | 1.08 | 0.33 |
Need to convert a specific frequency? Use our frequency-to-wavelength calculator for exact conversions.
Frequently Asked Questions
What does 468 divided by frequency mean?
The formula 468/f(MHz) gives the total length of a half-wave dipole antenna in feet. The number 468 comes from the speed of light converted to feet-per-second, divided by two (for a half wavelength), and then reduced by about 5% to account for the end effect, the way current behaves at the tips of a real wire antenna. This correction means the antenna resonates slightly shorter than a pure half wavelength in free space.
How long is a half-wave dipole for 2 meters?
For the 2-meter band at 146 MHz, a half-wave dipole is about 3.2 feet (0.98 meters) total, with each leg approximately 1.6 feet (0.49 meters). This compact size is one reason the 2-meter band is so popular for portable and home station use.
Do I need to add extra wire when cutting a dipole?
Yes. Always cut your antenna wire 2-3% longer than the calculated length. You can then trim small amounts from each end and re-check your SWR after each trim. It is much easier to shorten an antenna than to splice wire back on. A good SWR meter or antenna analyzer is essential for this process.