Dipole Antenna Calculator — Half-Wave Dipole Length
A half-wave dipole is the simplest resonant antenna: its total length equals half the wavelength at the operating frequency. Enter the frequency and the velocity factor of your wire, and get the exact cut lengths for the full dipole and each arm.
MHz
Full dipole length (each arm is half this)
- 1
Frequency in Hz
100 MHz × 10⁶ = 100,000,000 - 2
Free-space wavelength
c ÷ f = 299,792,458 ÷ 100,000,000 = 2.9979 - 3
Effective wavelength (× VF)
2.9979 × 0.95 = 2.848 - 4
Half-wave dipole length (÷ 2)
2.848 ÷ 2 = 1.424Total dipole length equals half the effective wavelength.
How does this calculator work?
For a half-wave dipole, total length = (c × VF) / (2 × f). With bare wire (VF ≈ 0.95) this simplifies to roughly 142.65 / f_MHz metres. Each arm is half the total. Feed-point impedance ≈ 73 Ω at resonance. Adjust VF for your wire insulation type.
Formula
How this is calculated
A dipole antenna resonates when its total length equals half the wavelength of the signal it is meant to radiate or receive. The free-space wavelength is λ = c / f, where c is the speed of light (≈ 299,792,458 m/s) and f is the frequency in hertz. However, electrical signals travel slightly slower in real wire than in free space, so the effective wavelength is shorter: λ_eff = λ × VF, where VF (velocity factor) is typically 0.95 for bare copper wire and 0.80–0.95 for insulated wire.
The full dipole length is λ_eff / 2. The antenna is split at the centre feed-point into two equal arms, each of length λ_eff / 4. A practical rule of thumb for bare wire in metres is L ≈ 142.65 / f_MHz (which already embeds VF ≈ 0.95), but this calculator lets you set VF explicitly for your wire type.
At resonance, the feed-point impedance of a half-wave dipole in free space is approximately 73 Ω — well-matched to standard 75 Ω coaxial cable and close enough to 50 Ω systems with a matching network. Real-world impedance varies with height above ground, surrounding objects, and the wire diameter.
Frequently asked questions
The velocity factor (VF) is the ratio of the wave speed in the antenna wire to the speed of light in free space. Bare copper wire is typically 0.95–0.97; insulated wire is lower (≈0.80–0.95 depending on insulation thickness and dielectric constant). Using VF correctly ensures the physical cut length matches the resonant electrical length.
Yes — enter frequencies below 1 MHz (e.g. 0.5 for 500 kHz) or above 1000 MHz for UHF by just typing the value. The formula is the same; the result will be a very long wire at low frequencies and a very short element at microwave frequencies.
A half-wave dipole in free space presents approximately 73 Ω at resonance. Height above ground, nearby structures, and wire diameter all shift this value. Most practical installations use 50 Ω or 75 Ω coax with a balun or matching network to handle the mismatch.
TG we-Calculate Editorial Team. (2026). Dipole Antenna Calculator — Half-Wave Dipole Length [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/dipole-calculator
TG we-Calculate Editorial Team. "Dipole Antenna Calculator — Half-Wave Dipole Length." TG we-Calculate. 2026. https://we-calculate.com/calculator/dipole-calculator.
TG we-Calculate Editorial Team, "Dipole Antenna Calculator — Half-Wave Dipole Length," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/dipole-calculator
@misc{wecalculate_dipole_calculator, title = {Dipole Antenna Calculator — Half-Wave Dipole Length}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/dipole-calculator}}, year = {2026}, note = {TG we-Calculate} }
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