Dipole Antenna Calculator
Enter frequency in MHz or GHz. Use band presets below for common amateur and commercial frequencies.
Accounts for conductor type and insulation. Default 0.95 suits bare copper wire.
Applies an additional ~3% length correction for insulated wire antennas.
Enter a Frequency to Begin
Select your target frequency and antenna type above. The calculator will instantly show total length, each leg, wavelength reference values, feedpoint impedance, and a comparison chart across all antenna types.
Ham Radio Band Reference Table (Half-wave Dipole)
| Band | Frequency | Total (ft) | Total (m) | Leg (m) |
|---|---|---|---|---|
| 160m | 1.9 MHz | 246.3 | 75.08 | 37.54 |
| 80m | 3.75 MHz | 124.8 | 38.04 | 19.02 |
| 60m | 5.3325 MHz | 87.8 | 26.75 | 13.38 |
| 40m | 7.15 MHz | 65.5 | 19.95 | 9.98 |
| 30m | 10.125 MHz | 46.2 | 14.09 | 7.04 |
| 20m | 14.175 MHz | 33.0 | 10.06 | 5.03 |
| 17m | 18.1 MHz | 25.9 | 7.88 | 3.94 |
| 15m | 21.225 MHz | 22.0 | 6.72 | 3.36 |
| 12m | 24.94 MHz | 18.8 | 5.72 | 2.86 |
| 10m | 28.85 MHz | 16.2 | 4.94 | 2.47 |
| 6m | 51 MHz | 9.2 | 2.80 | 1.40 |
| 2m | 146 MHz | 3.2 | 0.98 | 0.49 |
| 70cm | 435 MHz | 1.1 | 0.33 | 0.16 |
| CB | 27 MHz | 17.3 | 5.28 | 2.64 |
| FM | 98 MHz | 4.8 | 1.46 | 0.73 |
How to Use This Calculator
Enter Your Target Frequency
Type the frequency in the input field. You can enter values in MHz (e.g., 14.175 for the 20-meter ham band) or switch to GHz for microwave frequencies. Use the quick band preset buttons to instantly load popular amateur radio bands, CB, FM broadcast, or WiFi frequencies.
Select Antenna Type and Velocity Factor
Choose your antenna configuration: Half-wave Dipole (most common), Folded Dipole (300Ω, used with 4:1 balun), Inverted Vee (single support, omnidirectional), or Full-wave Dipole (NVIS/low-angle). Then select the velocity factor matching your conductor — bare copper wire is 0.95, metal tubing is 0.98, insulated wire is 0.93. Enable the Insulated Wire toggle if your wire has a plastic jacket for an additional 3% correction.
Read Your Antenna Dimensions
Results appear instantly showing total antenna length and each leg length in both feet and meters. The visual dipole diagram illustrates the physical layout with the feed point marked at center. Wavelength reference values (full, half, and quarter wavelength) are shown for designing matching sections or related antenna elements.
Check Feedpoint Info and Build Longer
Review the feedpoint impedance, recommended balun type, and coaxial cable recommendation for your antenna type. When cutting wire, always add 5–10% extra length and trim gradually while measuring SWR. Export your results to CSV for field notes, or print the page for reference during antenna construction.
Frequently Asked Questions
Why is the dipole formula 468/f instead of 492/f?
The theoretical free-space half-wavelength of a wire antenna is 492 divided by frequency in MHz (in feet). However, real wires experience an 'end effect' caused by increased capacitance near the wire tips, which shortens the physical length needed for resonance compared to the free-space ideal. Multiplying 492 by a typical end-effect correction factor of 0.95 gives approximately 468. This empirical constant was established through decades of practical antenna measurement and is accurate for thin wire antennas (14–18 AWG) at typical installation heights. Thicker conductors like aluminum tubing use a slightly higher factor (0.97–0.98), while heavily insulated wire may need values as low as 0.93.
What is velocity factor and why does it matter for antenna length?
Velocity factor (k) describes how fast an electromagnetic wave travels along a conductor relative to the speed of light in free space. Bare copper wire has a velocity factor of approximately 0.95 — meaning RF travels at 95% of the free-space speed. Insulated wire is slower (0.93) because the dielectric material of the insulation slows the wave. Coaxial cable inner conductor can be as low as 0.66. Since the physical antenna length for resonance equals the electrical half-wavelength multiplied by the velocity factor, using an incorrect value results in an antenna that is too long or too short, producing elevated SWR. Always select the velocity factor that matches your actual conductor type.
What is the difference between a folded dipole and a standard dipole?
A standard half-wave dipole consists of a single wire fed at the center, presenting approximately 73 ohms at the feedpoint. A folded dipole uses the same physical wire length but the wire is bent back on itself to form a narrow loop with two parallel conductors connected at both ends. This parallel current path multiplies the feedpoint impedance by a factor of four, producing approximately 300 ohms. This impedance is a perfect match for 300-ohm twin-lead transmission line, which was once the standard for TV and FM antennas. With a 4:1 balun, it can also feed 75-ohm coax. Folded dipoles are also commonly used as the driven element in Yagi-Uda directional antennas due to their broader impedance bandwidth.
Why is an inverted vee shorter than a horizontal dipole?
An inverted vee hangs its two legs downward from a central apex point at an angle, rather than running horizontally. When legs are not horizontal, their effective electrical length is reduced because the component of the electromagnetic field coupling changes with the angle. The commonly used formula constant for an inverted vee is 449 (versus 468 for a horizontal dipole), representing approximately a 4% reduction. Additionally, the inverted vee's legs being closer to ground means ground proximity effects are stronger, which also shifts resonance slightly. The feed-point impedance of an inverted vee is approximately 52 ohms — a much closer match to 50-ohm coax than the 73-ohm horizontal dipole, making it possible to operate without a balun in some installations.
Do I need a balun on my dipole antenna?
A current balun (1:1) is strongly recommended for dipole antennas even though the antenna can operate without one. Without a balun, RF current can flow on the outside of the coaxial cable shield back toward the transmitter, causing common-mode interference, RF in the shack, erratic SWR readings, and potential touch-hazard. A 1:1 current balun placed at the feedpoint prevents this by forcing equal and opposite currents in each dipole leg. For folded dipoles, a 4:1 voltage balun transforms the 300-ohm feedpoint impedance down to 75 ohms for coax matching. Choose a balun rated for at least twice your transmitter output power. Commercial ferrite choke baluns are compact and effective; DIY coax-wound choke baluns using RG-8X or similar are also popular among amateur radio operators.
How does antenna height above ground affect resonant length?
Height above ground significantly affects dipole resonant frequency and feedpoint impedance. At very low heights (less than 0.1 wavelength above ground), ground coupling dramatically lowers the resonant frequency and changes feedpoint impedance, often requiring a shorter antenna than the formula predicts. At typical amateur radio heights of 0.25 to 0.5 wavelengths, the 468/f formula gives a reasonable starting point. Above about one wavelength, free-space values are approached closely. Ground conductivity also plays a role — dry sandy soil is a poor reflector while salt water is an excellent one, each producing different impedance and resonant frequency shifts. For HF operation, the general advice is to install the antenna as high as practical, measure SWR with an antenna analyzer, and trim to resonance at your actual installation height.