Dipole Antenna Length Calculator

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

About Dipole Antenna Length Calculator

A half-wave dipole is about 0.95 x lambda/2 long in practice, split into two equal legs. Its feed impedance is 73 ohms in free space but varies strongly with height above ground, dropping toward 40 ohms below a quarter wavelength and peaking above it — which is why SWR changes when a dipole is raised.

Formula

Dipole length

total = 0.5 x lambda x 0.95; each leg is half of that; 143 / f(MHz) metres is the handy shortcut

Worked example

With the default values below, Dipole Antenna Length Calculator returns Total dipole length of 20.06. Change any input above and every figure here is recalculated in your browser.

Inputs used

Frequency: 7.1 MHz
End-effect factor: 0.95
Height above ground: 10 m

Results

Total dipole length: 20.06 m
Each leg: 10.03 m
Height in wavelengths: 0.237 λ
Estimated feed impedance: 55 Ω

Step by step

1Values used
2Dipole length
3Total dipole length= 20.06 m
4Each leg= 10.03 m
5Height in wavelengths= 0.237 λ
6Estimated feed impedance= 55 Ω

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 3 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

What is the quick formula?

Total length in metres is about 143 divided by frequency in MHz, or 468 divided by frequency in MHz for feet.

Why does height change the impedance?

Ground reflection couples back into the antenna, adding or subtracting from the radiation resistance depending on the phase, which depends on height in wavelengths.