How is half-wave dipole length estimated?

The calculator divides the exact free-space wavelength by two, then multiplies it by the selected practical length factor. Each dipole element is half of that total.

Why is the default length factor 0.95?

A 95% factor is a common starting estimate for practical end effects, but it is not universal. The factor is editable because construction and environment change the final tuned length.

What does trimming allowance do?

It adds a user-selected percentage to each initial cut without changing the calculated target. Starting slightly long leaves material available for tuning.

Will the calculated antenna resonate exactly?

No. Conductor, insulation, height, surroundings, ground, nearby metal, feedpoint construction, and feedline effects can all shift resonance. Measure and tune the completed antenna.

Dipole Antenna Length Calculator

Estimate a center-fed half-wave dipole's total and per-element starting dimensions, compare them with the ideal wavelength, and add optional trimming allowance.

Dipole Antenna Length Calculator

Estimate a center-fed half-wave dipole's total and per-element starting dimensions, compare them with the ideal wavelength, and add optional trimming allowance.

Center-fed half-wave dipole

Practical starting dimensions

Estimated dipole length

1.424 mTotal tip-to-tip starting length at 100 MHz

Cut each side to approximately712 mm

Frequency: 100 MHz
Full wavelength: 2.998 m
Ideal half wave: 1.499 m
Length factor: 95%

Build measurements

From wavelength to cut length

Ideal half wave1.499 m

Practical reduction74.95 mm

Calculated leg712 mm

Initial cut with allowance712 mm

A starting estimate, not guaranteed resonance. Build slightly long when practical, then measure and tune the completed antenna for its installation.

Formula reference

Half-wave dipole relationships

Free-space wavelength

λ = c / f

The shared RF engine uses 299,792,458 m/s.

Practical total length

L = (λ / 2) × K

K is the editable practical length factor.

Each element

E = L / 2

Both legs are equal before final physical tuning.

Conductor diameter and insulation, nearby materials and metal, mounting height, ground, feedpoint construction, balun or feedline effects, and construction tolerances can all shift resonance. This calculator does not estimate SWR, impedance, gain, pattern, or bandwidth.