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Antenna Length Calculator

Find the right antenna length for a frequency.

Result

0.5137 m
1.0274 m
2.0548 m

How it is calculated

Radio waves travel at about 300 million m/s, so with the frequency in MHz the wavelength in metres is λ = 300 ÷ f. The tool shows the full wavelength, the half-wave length λ ÷ 2 (a classic dipole) and the quarter-wave length λ ÷ 4 (a ground-plane or whip antenna), each to four decimals in metres. The result is the length in free space; a real antenna is usually cut a few percent shorter because of the velocity factor of the wire and end effects, so trim while tuning. Frequency must be above zero.

Worked example

For the 2 m amateur band at 146 MHz: λ = 300 ÷ 146 = 2.0548 m. Half-wave = 2.0548 ÷ 2 = 1.0274 m. Quarter-wave = 2.0548 ÷ 4 = 0.5137 m, about 51 cm for a whip.

Try this example →

Common mistakes

  • Entering the frequency in Hz or kHz; the tool needs MHz, so 146 MHz is 146, not 146000000.
  • Cutting the element exactly to the printed length; real antennas are normally shortened by a few percent and fine-tuned with an SWR meter.
  • Mixing up the quarter-wave figure for one whip element with the half-wave figure for the full dipole, which is made of two quarter-wave arms.
  • Forgetting that a quarter-wave whip needs a ground plane to work properly.
  • Using the middle of a band without checking: the length is exact for one frequency only.

About this calculator

Radio wavelength relates to frequency by λ = c/f; since the speed of light c ≈ 3×10⁸ m/s, this simplifies to the handy rule λ (meters) = 300 / f (MHz). From that wavelength, this calculator derives the three most common antenna lengths: full-wave (λ), half-wave (λ/2 — the classic dipole), and quarter-wave (λ/4 — the classic ground-plane monopole), often scaled by a velocity factor of roughly 0.95 to account for a real wire's end effects.

Amateur (ham) radio operators use these formulas to cut dipole and monopole wire antennas tuned to a specific band, and RF and broadcast engineers use the same relationship when designing antennas for transmitters and receivers across the spectrum, from HF ham bands up through VHF/UHF. Enter a target frequency in MHz to get all three lengths at once.

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