Enter Frequency
Formula
Full wave = (c × velocity factor) / f
Half wave = λ / 2 Quarter wave = λ / 4
The default 0.95 factor shortens the free-space length to provide a reasonable starting point for many wire or rod elements.
Worked Example
At 146 MHz with a 0.95 velocity factor, a quarter-wave element is about 0.488 m or 19.2 inches.
Builders normally cut slightly long, install the antenna in its actual environment, then trim while measuring resonance or SWR.
Assumptions and Limits
Element diameter, insulation, nearby metal, ground plane size, mounting position, feed method, and end effects all change the finished resonant length.
This is a starting dimension, not a guaranteed tuned antenna. Measure and adjust the completed antenna with suitable RF test equipment.