Dipole Antenna Length Calculator
Free half-wave dipole antenna length calculator. Uses L = 468/f (feet) or 142.65/f (meters). Get wavelength, leg length, and charts for ham radio and RF.
About This Calculator
The Dipole Antenna Length Calculator computes the physical dimensions of a half-wave dipole antenna — the most widely used antenna design in amateur radio, FM broadcasting, and shortwave communication. By entering your operating frequency in megahertz (MHz), you instantly receive the total antenna length, each leg's length, and the corresponding wavelength values in both metric (meters) and imperial (feet) units.
The calculator uses the standard empirical formula L = 468 / f (feet) or L = 143 / f (meters), which has been the trusted standard in antenna design for over a century. This formula accounts for the velocity factor of typical wire conductors — radio waves travel approximately 5% slower in wire than in free space, which is why the practical formula differs from the theoretical half-wavelength of 492/f. The leg length of each dipole element equals half the total length (L/2), as each pole of the dipole forms one quarter of the operating wavelength.
The half-wave dipole antenna offers approximately 73 ohms of feed-point impedance at resonance, making it an excellent match for standard 50-ohm or 75-ohm coaxial cable with minimal impedance matching. It provides a clean radiation pattern with maximum signal strength perpendicular to the antenna axis, and it is the reference antenna for many gain measurements (dBd — decibels relative to a half-wave dipole).
Regional Notes
United States: The FCC regulates amateur radio frequencies under Part 97. Popular ham bands include 160m (1.8-2.0 MHz), 80m (3.5-4.0 MHz), 40m (7.0-7.3 MHz), 20m (14.0-14.35 MHz), and the FM broadcast band (88-108 MHz). The ARRL provides guidance on antenna construction and safety.
United Kingdom: Ofcom regulates amateur radio in the UK under the Amateur Radio Licence. Popular bands include 80m (3.5-3.8 MHz), 40m (7.0-7.2 MHz), and 20m (14.0-14.35 MHz). The RSGB offers extensive resources for antenna design and construction for UK amateurs.
India: The WPC (Wireless Planning and Coordination Wing) under the Department of Telecommunications handles amateur radio licensing. Popular bands include 40m (7.0-7.2 MHz) and 20m (14.0-14.35 MHz). The Amateur Radio Society of India (ARSI) supports the ham radio community with educational resources.
Frequently Asked Questions
How do I calculate the length of a dipole antenna?
To calculate dipole antenna length, use the formula L = 468 / f where L is the total antenna length in feet and f is the desired frequency in megahertz (MHz). For metric, use L = 143 / f to get length in meters. The leg length of each dipole element is half the total length (L/2).
What is the formula for dipole antenna length?
The standard dipole antenna length formula is L = 468 / f for feet, or L = 143 / f for meters, where f is the frequency in MHz. These formulas are derived from the half-wave dipole principle where the antenna length equals half the wavelength, adjusted for the velocity factor of the conductor (about 0.95).
How long is a dipole antenna for 20 meters (14 MHz)?
For the 20-meter amateur radio band at 14 MHz, the total dipole antenna length is approximately 10.21 meters (33.43 feet), and each leg is about 5.11 meters (16.71 feet). This uses the formula L = 143 / f, giving L = 143/14 = 10.21 m.
What is the difference between a dipole and a half-wave dipole?
A half-wave dipole is the most common type of dipole antenna where the total length equals half the wavelength at the operating frequency. The term dipole technically refers to any antenna with two poles, but in practice 'dipole antenna' typically means a half-wave dipole. The half-wave dipole offers a good balance of efficiency, impedance (approximately 73 ohms), and ease of construction.
Can I use this calculator for FM broadcast frequencies?
Yes, the dipole antenna length calculator works for any frequency including FM broadcast (88-108 MHz). For 100 MHz FM, the antenna length is 1.43 meters (4.68 feet) total, with each leg measuring 0.715 meters (2.34 feet). The calculator provides both metric and imperial measurements for your convenience.
How does conductor diameter affect dipole antenna length?
Conductor diameter affects the antenna length through the velocity factor. Thicker conductors have a lower velocity factor, requiring slightly shorter antennas. The standard formula L = 468/f assumes a typical thin wire. For thick conductors or tubes at high frequencies, an adjustment factor k can be applied, calculated from the ratio of the half-wavelength to conductor diameter.
What is the wavelength of a dipole antenna?
The wavelength of a dipole antenna is calculated as λ = c / f, where c is the speed of light (299,792,458 m/s) and f is the frequency in Hz. The half-wave dipole total length equals λ/2, and each leg equals λ/4. For example, at 7 MHz, λ = 42.83 m, the antenna length is 21.41 m (λ/2), and each leg is 10.71 m (λ/4).
Why is the dipole calculator formula 468/f instead of 492/f?
The theoretical half-wave length is 492/f (in feet), but the practical formula 468/f accounts for the velocity factor of real conductors (typically 0.95). The velocity factor depends on the conductor material and diameter — radio waves travel slower in wire than in free space. The 468/f formula is the empirical standard derived from decades of amateur radio and professional antenna construction experience.