Dipole / Monopole Antenna Length Calculator

Common calculator for half-wave dipole and quarter-wave monopole. Choose antenna type and either compute length from frequency or estimate resonant frequency from length.

Inputs

Mode Antenna Type

Frequency

Shortening factor (end-effect / velocity factor)

Results will appear here.

Diagrams & Theory

Wire Antenna Sketches

Key Formulas

λ = c / f

L_dipole ≈ (λ / 2) · k

L_monopole ≈ (λ / 4) · k

Inverse (Length → Resonant Frequency)

f ≈ c / (2·L / k) for dipole (λ/2 type)

f ≈ c / (4·L / k) for monopole (λ/4 type)

Symbol Glossary

c – speed of light ≈ 3×10⁸ m/s
f – resonant frequency (Hz)
λ – wavelength in free space (m)
L – total physical length of the radiator (dipole) or vertical element (monopole)
k – shortening factor (< 1) accounting for end effects, wire thickness, insulation, etc.

Design Notes

Formulas assume free-space or far from ground objects. Real installations detune the antenna.
For typical thin-wire HF/VHF dipoles in air, k ≈ 0.95 is a good starting value.
Monopoles are above a ground plane or vehicle body; effective height depends strongly on ground size.
Final tuning is almost always required in practice (trimming length and measuring VSWR).