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Antenna Length Calculator

Work out antenna length instantly with clear inputs, formula shown and shareable results.

About Antenna Length Calculator

Wavelength is the speed of light divided by frequency, and a resonant element is a simple fraction of it. Real conductors are slightly shorter than the free-space figure because of end effect and conductor diameter, which is what the velocity factor of about 0.95 accounts for.

Formula

Antenna length

lambda = c / f; element = lambda x fraction x velocity factor

Worked example

With the default values below, Antenna Length Calculator returns Element length of 0.49. Change any input above and every figure here is recalculated in your browser.

Inputs used

Frequency
145 MHz
Antenna typeone of Quarter wave (ground plane), Half wave dipole, Full wave loop, 5/8 wave vertical
Quarter wave (ground plane)
Velocity factor
0.95

Results

Element length
0.49 m
Element length
49.10 cm
Free-space wavelength
2.07 m
Element length
19.33 in

Step by step

  1. 1Values used
  2. 2Antenna length
  3. 3Element length= 0.49 m
  4. 4Element length= 49.10 cm
  5. 5Free-space wavelength= 2.07 m
  6. 6Element length= 19.33 in

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or fees or charges into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

Frequently Asked Questions

Why is a real dipole shorter than half a wavelength?

End capacitance and the finite conductor thickness make it electrically longer than its physical length, so it must be trimmed by roughly 5%.

What does the 5/8 wave vertical gain?

It concentrates radiation closer to the horizon, giving about 3 dB over a quarter wave, but needs a matching network because it is not resonant.

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