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Wavelength calculator

Where band names come from

“Two metres”, “forty”, “twenty” — those are the wavelengths in metres. 145 MHz gives about 2 m, 7 MHz about 40 m. Knowing λ you can size an antenna at once: a half-wave dipole is λ/2, a quarter-wave whip λ/4.

λf = 145 MHz · in a cable the wave is shorter by a factor of √ε
λ = c / f — the wavelength in free space
Frequency → wavelength
Frequency
Wavelength (λ)
Wavelength → frequency
Wavelength (λ)
Frequency

📐 The formulas​

Wavelength:

λ [m] = 299.792458 / f [MHz]

Frequency:

f [MHz] = 299.792458 / λ [m]

Symbols:​

  • λ — wavelength in free space
  • f — frequency
  • 299.792458 — the speed of light in m·MHz
Where this calculator stops:
  • The calculation is for free space; in cable or dielectric the wave is shorter by a factor of √ε
  • A real resonant element is about 5 % shorter than a geometric λ/2, because of the end effect
  • A thick conductor shortens the element more than a thin one

🎯 In practice​

Typical dimensions in terms of λ:​

ElementLength
Half-wave dipoleλ/2 × 0.95
Quarter-wave whipλ/4 × 0.95
Yagi element spacing0.15…0.25 λ
Antenna height above groundfrom λ/2
Practical advice:
  1. For quick mental arithmetic: λ [m] ≈ 300 / f [MHz] — the error is under 0.1 %.
  2. Work out cable section lengths not here but in the transmission line length calculator, which applies the velocity factor.
  3. Always start antenna dimensions from λ and only then apply corrections for conductor thickness and proximity to ground.

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UR3PKI. «Wavelength calculator». CyberDev.Space. https://cyberdev.space/en/radio/calculators/others/wavelength (licence CC BY-NC-SA 4.0).

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