Dipole Antenna Length
Half-wave dipole, quarter-wave vertical or full-wave loop length for a frequency with your velocity factor — each leg in m, ft and in, band trim, 3rd harmonic.
Wavelength, total and per-leg lengths in m, ft and in, the equivalent ft-formula constant (468 ÷ f style), how much to trim between two band edges, and the same antenna at three times the frequency.
Example: 14.2 MHz: λ 21.11 m, half-wave dipole 10.03 m (32.9 ft, 5.01 m per leg) at VF 0.95 — the 468 ÷ f rule; across 14.0–14.35 MHz the length changes 24.8 cm, so cut long and trim.
Half a wavelength,
a little shorter in wire.
Where the length comes from, what the velocity factor covers, and why the result is a starting point.
The length
A half-wave dipole is resonant when each leg is a quarter wavelength; λ = c/f with c = 299 792 458 m/s, so at 14.2 MHz λ is 21.11 m. Wire is not free space: end effects, wire diameter and insulation make the resonant length a few percent shorter, expressed as a velocity factor — 0.95 is the usual starting point for bare wire in air, and the well-known 468/f (MHz) feet rule is exactly a factor of 0.951. A quarter-wave vertical is half a dipole worked against radials; a full-wave loop has a circumference of one λ.
Band and harmonics
Over a band the length changes in inverse proportion to frequency; the trim figure is the difference between the low and high band-edge lengths — cut for the low end, then shorten. At three times the frequency a dipole is also resonant (three half-waves), which is why a 40 m dipole works on 15 m; the 3rd-harmonic figure shows that antenna's length.
Trimming
Height above ground, nearby metal, insulators and the feed point all shift resonance, so treat the number as a cutting length: cut slightly long, hang the antenna where it will live, and trim while watching SWR or an analyser. Nothing leaves the browser; the same four anonymous usage counts as the rest of the site apply.
SOURCES
- λ = c ÷ f with c = 299 792 458 m/s; element = ½ λ (dipole), ¼ λ (vertical), 1 λ (loop) × velocity factor; 468 ÷ f(MHz) ft corresponds to a factor of 0.951
Last reviewed 22 September 2026. How results are checked: How we verify.