Antenna Length Calculator

Heinrich Hertz demonstrated the first practical antenna in 1887 — a pair of metal spheres separated by a spark gap — while verifying Maxwell\'s 1865 prediction of electromagnetic radiation. Hertz\'s dipole antennas operated at the self-resonant frequency determined by their physical length, giving engineers the first experimental confirmation that wavelength and antenna size are directly linked by λ = c/f.

Guglielmo Marconi refined dipole and vertical antennas through the 1890s for commercial wireless telegraphy, culminating in his 1901 transatlantic transmission from Cornwall to Newfoundland. By the 1920s, radio amateurs had established the standard rule of thumb that this calculator uses: a quarter-wavelength monopole on a ground plane presents near 50Ω at resonance, making it the easiest match for typical RF transmitter output stages.

The velocity-factor concept (physical length slightly shorter than free-space wavelength due to end-effect capacitance and wire insulation) dates to the 1930s antenna research at RCA and Western Electric. John Kraus\'s 1950 textbook Antennas formalized the length corrections — typically multiplying by ~0.95 for insulated wire and ~0.98 for bare copper — and the same factors remain standard in ARRL and ITU antenna handbooks today.

Enter a frequency (Hz, kHz, MHz, or GHz) and velocity factor (0.95 for typical insulated wire, 0.98 for bare copper). The tool returns the full wavelength plus the three most common antenna lengths: quarter-wave (monopole on ground plane), half-wave (dipole), and 5/8-wave (enhanced low-angle gain vertical).

For most practical work, cut the wire 5–10% long, check SWR with an analyzer, and trim in small steps until resonance lands in your target band. Antennas near metal, buildings, or ground plane edges may need longer cuts (lower effective k). Everything runs client-side; no values leave your browser.