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Antenna Length Calculator

Calculate half-wave dipole and quarter-wave vertical antenna element length from frequency. Includes velocity factor correction for wire type.

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Inputs that matter
Frequency, Element Type
Output to expect
Antenna Length Calculator
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Reference & details

How it works

Half-Wave Dipole

Classic formula for wire dipole in free space. Each leg = total ÷ 2. Adjust shorter for insulated wire (velocity factor 0.95–0.98).

Total length (ft) = 468 ÷ Frequency (MHz)

Quarter-Wave Vertical

Quarter-wave vertical over ground plane. Ground radials improve efficiency. Multiply by velocity factor for coated or thick wire.

Length (ft) = 234 ÷ Frequency (MHz)

Velocity Factor Correction

Insulated wire: VF ≈ 0.95. Bare copper: 0.98–1.0. Coaxial elements use cable VF (typically 0.66–0.85).

Physical length = Calculated length × Velocity factor

Updated: July 2026

Example Scenarios

468 ÷ 7.150 = 65.5 ft total, 32.75 ft per leg. Trim 2–3% shorter and tune with SWR analyzer for lowest SWR at operating frequency.

234 ÷ 146 = 1.60 ft (19.2 inches) radiator length for quarter-wave ground plane with four radials.

Calculate separate dipole lengths for 80m, 40m, 20m segments connected to common feedpoint — each leg pair cut to band center frequency.

FAQ

Antennas near ground, buildings, and conductors appear electrically shorter. Start 5% long and trim for minimum SWR. Environmental factors require on-site tuning.

Ratio of signal speed in wire vs free space. Insulation slows propagation, requiring physically shorter elements. Check wire manufacturer specs for exact VF.

Half-wave dipole is most common HF antenna — simple, bidirectional, ~72 ohm feed impedance. Quarter-wave vertical needs ground radials but offers omnidirectional pattern.

Height affects radiation pattern and impedance, not physical length requirement. Higher mounting improves performance but element length stays frequency-dependent.

Use SWR analyzer or transceiver SWR meter. Trim equal amounts from each leg (inches at a time). Lower frequency resonance = antenna too long; shorten. Target SWR below 1.5:1.

About Antenna Length Calculator

Antenna element length is inversely proportional to frequency. Enter operating frequency and wire type to calculate half-wave dipole total length, each leg length, and quarter-wave vertical with velocity factor correction for insulated wire.