Antenna length & wavelength
Calculate wavelength and geometric starting estimates for antenna dimensions.
About this tool
Enter a positive frequency, its unit and a factor 0 < k ≤ 1. Decimal comma or point is accepted. Results update directly; invalid or incomplete inputs clear the results. Lengths select appropriate metric units, periods select time units. Values are geometric starting estimates, not an antenna optimization.
With exact c = 299792458 m/s, free-space λ = c/f. All geometric lengths use kλ: dipole total kλ/2, each of its two equal arms kλ/4, monopole kλ/4, vertical 5kλ/8, loop circumference kλ, and the retained eighth-wave kλ/8. Period is 1/f and does not depend on k. Changing the frequency unit reinterprets the entered number.
For a uniform medium, k can represent phase velocity divided by c. An antenna shortening factor can instead approximate end effects for a specific design. Cable velocity factor and antenna shortening are not interchangeable; one shared k cannot predict resonance of every geometry, feed arrangement, material or environment.
Details separately show the empirical total dipole rule L(ft) ≈ 468/f(MHz), its metric equivalent using exactly 0.3048 m/ft, and each arm of the k-based dipole. The empirical rule does not apply k again. At 145 MHz and k=0.95, the k-based total dipole is about 0.982079 m and each arm about 0.491039 m. Real antennas require measurement and tuning; no matching, impedance, losses, bandwidth or radiation pattern is calculated.