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Calculation Tools
Antenna Length Calculator
Compute practical element lengths for common HF/VHF/UHF antennas including velocity factor.
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Tool
Half-wave dipole (total)10.028 m / 32.90 ft
Dipole leg (each)5.014 m
Quarter-wave vertical5.014 m / 16.45 ft
Full-wave loop20.057 m / 65.80 ft
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How it works
A half-wave dipole is approximately λ/2 long, but real wire radiates a little slower than in free space, so the practical length uses the classic 468 / f(MHz) formula for feet (or 143 / f(MHz) for meters) which bakes in a ~0.95 velocity factor. A quarter-wave vertical is half of a dipole. A full-wave loop is ~1005 / f(MHz) feet.
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How to use
- Enter the design frequency in MHz.
- Set the velocity factor (0.95 is a typical bare wire value; drop to 0.90 for insulated wire).
- Read the total length for each antenna style; for a dipole, cut each leg to half of the total.
- Prune from long — start ~2% long, trim in small steps while checking SWR.
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Frequently asked questions
Why is my dipole not resonant at the calculated length?
Height above ground, nearby objects, and wire insulation all shift resonance. Always trim from long.
Does this handle traps or loading coils?
No — it covers straight-element antennas. Loaded antennas need model-specific formulas.