Antenna Length Calculator
Resonant antenna formulas
In free space, wavelength is the ratio of the speed of light to the operating frequency:
For practical antennas, builders often need quarter-wave or half-wave segments. Applying a velocity factor that captures dielectric loading leads to
where equals 4 for quarter-wave monopoles and 2 for half-wave dipoles. This calculator uses 300 m/ยตs as the speed of light when frequency is given in megahertz, delivering lengths directly in meters.
Example lengths
The table compares quarter-wave and half-wave lengths for common amateur bands assuming a velocity factor of 1.0. Adjust the form to see how insulation or tubing changes each value.
| Band | Frequency (MHz) | Quarter-wave (m) | Half-wave (m) |
|---|---|---|---|
| 40 m amateur | 7.1 | 10.56 | 21.13 |
| 2 m amateur | 146 | 0.51 | 1.03 |
| 70 cm amateur | 440 | 0.17 | 0.34 |
Remember that ground-plane spacing, feed matching, and conductor diameter further influence performance. Use the calculator as a starting point before trimming elements during tuning.