Antenna Length Calculator
Enter your target operating frequency. Use MHz for HF/VHF, or switch to GHz for microwave bands.
Wire or tubing diameter in millimeters. Affects the end-effect correction (k factor). Typical hookup wire is 1–2 mm; aluminum tubing is 6–25 mm.
Enter Frequency to Calculate
Select an antenna type, enter your operating frequency (or click a ham band preset), and the calculator will instantly show element lengths in both feet and meters.
How to Use This Calculator
Select Your Frequency
Type your target operating frequency in the Frequency field and choose MHz or GHz. Alternatively, click one of the ham band quick-select buttons (160m through 70cm) to load the center frequency of that band automatically.
Choose Your Antenna Type
Click the antenna type that matches what you want to build: Half-Wave Dipole for a basic horizontal wire antenna, Quarter-Wave Vertical for a ground-plane antenna, Full-Wave Loop for a wire loop, Inverted Vee for a center-supported dipole with drooping legs, 5/8-Wave Vertical for higher gain mobile or base antennas, or 3-Element Yagi for a directional beam antenna.
Adjust Advanced Inputs
Enter your conductor diameter in millimeters for a more accurate end-effect correction factor (k). If you are building a full-wave loop, enter the velocity factor of your coaxial matching section (0.66 for standard polyethylene coax, 0.80 for foam coax). The calculator updates all results automatically as you type.
Read Results and Build
Note the total length and element or leg length in both feet and meters. For Yagi antennas, record all element lengths and spacings. Use the comparison chart to see how your chosen type relates to other antenna types at the same frequency. Export to CSV for your logbook, or print the results page before heading to the workshop.
Frequently Asked Questions
Why does the calculator give a different length than the simple 468/f formula?
The classic 468/f formula for dipoles in feet already incorporates an end-effect correction of approximately 5 percent, reducing the theoretical free-space half-wavelength of 492/f to 468/f. This calculator goes one step further by adjusting the correction factor based on your conductor diameter. Thin wire has a slightly higher ratio of length to diameter, which increases the end effect and may require a lower k factor (and therefore a slightly shorter length), while thick aluminum tubing used in VHF arrays has a lower ratio and needs less correction. For most HF wire antennas using standard hookup wire (1–2 mm), the difference from the classic formula is small — typically less than 1 percent — but for precision VHF or UHF work it can be meaningful.
What is the difference between a dipole and an inverted Vee?
Both are half-wave center-fed antennas, but while a dipole has both legs horizontal, an inverted Vee has both legs sloping downward from a central apex, forming a V shape when viewed end-on. The downward angle of the legs changes their effective electrical length — the horizontal component of the wire interacts with the ground differently than a purely horizontal wire. As a result, inverted Vee legs need to be about 5 percent longer than dipole legs to achieve the same resonant frequency. The feed impedance also drops from about 73 ohms (free-space dipole) to approximately 52 ohms for an inverted Vee, making it a much better direct match to 50-ohm coaxial cable without a balun.
How many radials does a quarter-wave vertical need, and how long should they be?
A quarter-wave vertical requires a ground plane to complete the antenna circuit. The most common approach is to install at least four radial wires, each cut to a quarter wavelength, at the base of the vertical element. More radials improve efficiency: 16 buried radials give a significant improvement over 4, and professional broadcast towers use 120 radials. The radials do not need to be elevated — burying them 5 to 10 cm underground works well. For mobile installations on a vehicle, the metal vehicle body itself serves as the ground plane, which is why a quarter-wave whip on a car trunk lid works without any additional radials. The feed impedance of an ideal quarter-wave vertical over a perfect ground plane is approximately 36 ohms; real-world installations typically measure 50 ohms or slightly above, making them a good match to standard 50-ohm coax.
What are the advantages of a full-wave loop antenna?
A full-wave loop has several practical advantages over a simple dipole. Its total wire length (approximately 1005/f in feet) is the same regardless of whether you form it as a square, circle, or triangle, giving you flexibility to fit available space. The radiation pattern has a lower angle of radiation than a dipole at the same height, which generally means better DX (long-distance) performance on HF. The feed impedance is approximately 100 ohms, requiring a matching transformer or a quarter-wave coaxial section to feed with 50-ohm coax — this calculator computes the matching section length for you. Loop antennas also tend to be less sensitive to nearby objects than dipoles, making them practical for restricted installation spaces like small backyards or rooftops.
What gain does a 3-element Yagi provide, and is it better than a dipole?
A properly built 3-element Yagi provides approximately 7 to 9 dBi of forward gain, which is equivalent to 5 to 7 dBd (decibels over a dipole reference). In practical terms, this means your transmitted signal appears roughly 3 to 5 times stronger in the forward direction compared to a dipole running the same power. Equally important is the front-to-back ratio: a well-designed 3-element Yagi suppresses signals arriving from behind by 15 to 20 dB, which dramatically reduces interference from stations off the back of the beam. The trade-off is physical size — a 3-element Yagi for the 20-meter band has a boom around 3 to 4 meters long and requires a rotator to point it toward desired stations. For the 2-meter VHF band, the same design fits in a compact package less than a meter in length, making it ideal for satellite work or weak-signal EME (moonbounce) communication.
Why should I build the antenna longer and then trim it down?
Every real-world installation differs from the free-space model assumed by antenna length formulas. The height of the antenna above ground, soil conductivity at your location, nearby metal structures, tree foliage, and the presence of wire insulation all shift the actual resonant frequency from the calculated value. These effects almost always make the antenna resonate lower in frequency than predicted, meaning the antenna is effectively electrically too long. Starting longer guarantees you can trim the antenna down to the correct resonant frequency. If you start at exactly the calculated length and your antenna turns out to resonate too high in frequency (uncommon but possible at certain heights), you would need to splice in additional wire — a much harder repair. The 5 to 10 percent margin is a well-established rule of thumb in amateur radio construction practice, recommended by the ARRL Antenna Handbook and every major antenna building guide.