How this calculator works
A half-wave dipole has two approximately quarter-wave arms. End effects make its resonant physical length somewhat shorter than half a free-space wavelength. The common ARRL starting rule of 468 feet divided by frequency in MHz corresponds to a shortening factor near 0.952. Diameter, insulation, height and nearby objects all influence the final resonance. Diameter is reported as a slenderness ratio; it does not automatically determine the shortening factor in this model. Leave trimming allowance and measure the installed antenna.
Formula
lambda = c/f; L = k lambda/2; each leg = L/2; f = c k/(2L); measured k = 2Lf/c.
Worked example
At 299792458 Hz, free-space wavelength is exactly 1 m. With k = 0.95 the total dipole length is 0.475 m and each leg is 0.2375 m. With k = 1, a 1 m total length corresponds to 149896229 Hz.
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Frequently asked questions
Is the default factor exact?
No. It is a practical starting estimate. The best factor depends on conductor geometry, insulation and the antenna surroundings.
Does conductor diameter change bandwidth?
Yes. Thicker conductors generally affect impedance and resonance bandwidth. This simple length model only reports slenderness and leaves the shortening factor under your control.
Is the length measured along the wire?
Yes. The total is the sum of both conducting arms, excluding a feed-point gap or unmodelled loading elements.