Antenna Wavelength Calculator
Every antenna is designed around the wavelength of the radio frequency it is intended to receive or transmit. Wavelength and frequency are inversely related: as frequency increases, wavelength decreases. The relationship is given by lambda = c / f, where c is the speed of light (approximately 300,000,000 metres per second) and f is the frequency in hertz. From the full wavelength, engineers derive practical antenna dimensions. The half-wave dipole, two quarter-wave elements fed at the centre, is the most common wire antenna and forms the basis of many antenna designs. The quarter-wave monopole, used in car antennas and handheld radios, is a single element mounted over a ground plane that behaves electrically like a dipole. Real antennas are slightly shorter than theoretical free-space calculations because electromagnetic waves travel slower in conductors and insulating coatings than in free air, a correction applied via the velocity factor. Enter your frequency and unit below to instantly see the full wavelength, half-wave dipole length, and quarter-wave monopole length in metric and imperial units. A velocity factor note is included to guide practical construction.
Antenna lengths at 146 MHz
| Type | Meters (m) | Centimeters (cm) | Inches (in) |
|---|---|---|---|
| Full wavelength | -- | -- | -- |
| Half-wave dipole | -- | -- | -- |
| Quarter-wave monopole | -- | -- | -- |
Velocity factor note: practical wire antennas use approximately 0.95 VF (multiply lengths by 0.95). Coaxial cable elements use approximately 0.66 VF (multiply lengths by 0.66).
How antenna wavelength is calculated
The fundamental relationship between wavelength and frequency uses the speed of light in free space. Once the full wavelength is known, dipole and monopole lengths follow directly from it.
Frequency in Hz: f_hz = value × multiplier
Full wavelength: λ = 300,000,000 / f_hz (meters)
Half-wave dipole: L_half = λ / 2
Quarter-wave monopole: L_quarter = λ / 4
To cm: multiply by 100
To inches: multiply by 39.3701
Worked example: 146 MHz (2m band)
- Convert: 146 MHz = 146,000,000 Hz
- Full wavelength: 300,000,000 / 146,000,000 = 2.055 m
- Half-wave dipole: 2.055 / 2 = 1.027 m (102.7 cm, 40.45 in)
- Quarter-wave monopole: 2.055 / 4 = 0.514 m (51.4 cm, 20.23 in)
- With 0.95 VF wire correction: half-wave dipole = 1.027 × 0.95 = 0.976 m
Antenna wavelength: frequently asked questions
What is the wavelength formula for antennas?
The fundamental formula is: wavelength (lambda) = speed of light / frequency, or lambda = 300,000,000 / f_hz meters. For practical antennas, this free-space wavelength is then divided by 2 for a half-wave dipole or by 4 for a quarter-wave monopole. The speed of light figure (approximately 299,792,458 m/s) is rounded to 300,000,000 m/s for antenna calculations, which introduces less than 0.1% error.
What is velocity factor and why does it matter?
Velocity factor (VF) is the ratio of the speed of electromagnetic waves in a medium compared to free space. In free space VF = 1.0. For typical insulated wire antennas VF is approximately 0.95 to 0.97, meaning the physical antenna can be about 5% shorter than the theoretical free-space calculation. For coaxial cable used as an antenna element, VF drops to around 0.66 to 0.82 depending on the dielectric material. Applying the correct VF prevents your antenna from being resonant at the wrong frequency.
What is the difference between a dipole and a monopole antenna?
A dipole antenna is a balanced antenna consisting of two equal conductive elements fed at the centre, each a quarter wavelength long (total length = half wavelength). A monopole antenna is half of a dipole placed above a ground plane (real or simulated). The ground plane acts as a mirror image of the missing half. Common monopole types include the quarter-wave whip and the car roof-mount antenna. Dipoles are typically used for balanced, omnidirectional HF and VHF operation; monopoles are common on vehicles and base stations where a ground plane is available.
Which frequency bands are used in amateur (ham) radio?
In the United States, the FCC allocates numerous bands to amateur radio operators under Part 97. Major HF bands include 160m (1.8 to 2.0 MHz), 80m (3.5 to 4.0 MHz), 40m (7.0 to 7.3 MHz), 20m (14.0 to 14.35 MHz), 15m (21.0 to 21.45 MHz), and 10m (28.0 to 29.7 MHz). VHF bands include 6m (50 to 54 MHz) and 2m (144 to 148 MHz). UHF bands include 70cm (420 to 450 MHz). License class determines which portions of each band a licensee may use.
How do I prune an antenna to the correct length?
Antenna pruning (trimming) is the process of adjusting the physical length of an antenna to achieve resonance at your target frequency. Start by cutting the antenna slightly longer than the theoretical calculation (use a velocity factor of 0.95 for wire). Use an antenna analyser or SWR meter to measure resonance. If the resonant frequency is too low, shorten the antenna slightly and re-measure. Make small cuts (1 to 2 cm at a time for VHF, up to 5 cm for HF) and re-check until SWR is minimised at your target frequency.
Official sources
- FCC: Federal Communications Commission (fcc.gov)
- ARRL: American Radio Relay League antenna handbook (arrl.org)
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology. General reference, not a substitute for licensed engineering advice.