Antenna Length Calculator
Enter your operating frequency and tuning factors to estimate practical antenna element lengths for HF/VHF builds.
How this antenna calculator length tool works
This tool gives you quick, practical starting lengths for common antenna types using your selected frequency. It calculates full-wave, half-wave, and quarter-wave dimensions, then applies tuning factors so you can cut close to the target and fine-tune with an analyzer.
No calculator can replace real-world tuning because nearby metal, height above ground, and insulation all shift resonance. Still, this will get you very close, especially for dipoles and simple verticals.
Core antenna length formulas
1) Wavelength in meters
λ (meters) = 300 / frequency(MHz)
This is the ideal free-space wavelength. Everything else starts from this value.
2) Electrical length with velocity factor
adjusted wavelength = λ × velocity factor
Velocity factor accounts for how electromagnetic waves travel in real conductors and materials compared with vacuum/free space.
3) Practical element lengths
- Half-wave element: adjusted wavelength / 2
- Quarter-wave element: adjusted wavelength / 4
- Dipole total length: half-wave × shortening factor
- Dipole leg length: dipole total / 2
How to use it step by step
- Pick a preset band or manually enter a frequency in MHz.
- Set velocity factor (start with 0.95 for insulated wire).
- Set shortening factor (95% is a common practical baseline).
- Click Calculate Lengths.
- Cut your antenna slightly longer than the result and trim for lowest SWR.
Practical antenna building tips
Always cut long first
It is easy to shorten wire, but adding length back cleanly is harder. Start 2% to 5% long, then trim equally from both sides (for dipoles).
Height changes resonance
Antenna height above ground can shift your resonant frequency. Tuning at final installation height gives better real results than tuning close to ground.
Nearby objects matter
Gutters, towers, fences, and trees can detune an antenna. Keep radiator sections clear where possible, and re-check SWR after final mounting.
Quick reference starting points
| Band | Typical Center (MHz) | Quarter-Wave (Free Space) | Half-Wave Dipole Total (rule of thumb) |
|---|---|---|---|
| 40 meters | 7.1 | ~10.56 m (34.6 ft) | ~20.1 m (66.0 ft) |
| 20 meters | 14.2 | ~5.28 m (17.3 ft) | ~10.1 m (33.0 ft) |
| 10 meters | 28.4 | ~2.64 m (8.66 ft) | ~4.95 m (16.2 ft) |
| 2 meters | 146 | ~0.514 m (20.2 in) | ~0.96 m (37.8 in) |
Frequently asked questions
Is this calculator accurate for all antennas?
It is accurate as a starting-point estimator. Complex antennas (multi-band trapped designs, loaded coils, Yagis with parasitic elements) need design-specific formulas or modeling software.
What velocity factor should I use?
For many wire antennas, start around 0.95 to 0.98. If you know your exact wire and insulation properties, use measured or manufacturer values.
Why is my final tuned length shorter than calculated?
End effects, wire diameter, feed arrangement, and environment often shorten practical resonant lengths compared with ideal formulas. That is normal.
Final note
Use this antenna calculator length page to get your first cut right, then tune on-site with an SWR meter or analyzer for best performance. A few centimeters of trimming can make a big difference.