Antenna Length Calculator

Enter a frequency to get wavelength and common antenna lengths (¼, ½, 5/8, full). Add a shortening factor if needed.

How to Use

  1. Enter a frequency and select Hz/kHz/MHz/GHz.
  2. Select which antenna fraction you want (or “Show all”).
  3. Optional: enable the shortening factor for a practical starting cut.
  4. Use “Copy Results” to copy a clean summary, or “Share Link” to generate a restore URL.
Live Output
Computed in free-space, then multiplied by shortening factor (if enabled).
Wavelength (λ)
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Selected
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¼-wave
—
½-wave
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5/8-wave
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Full-wave
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Tip: Use the unit selector to switch display (m/ft/in). Shortening factor is optional.

Presets

One-click fills the frequency field. (No URL changes until Share.)

Show Work (step-by-step)
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Work uses: λ = c / f and L = λ × fraction × factor (factor defaults to 1.0).
Inputs & Settings
Fast, deterministic math. No uploads. Works fully client-side.
Use center frequency for a band. Example: 146.52 MHz (2m simplex).
“Show all” fills every line. Use units to get cut lengths in the format you want.
This is a simple multiplier. It helps estimate a practical starting cut length, but real antennas still require trim/tune.
Default is speed of light in vacuum. Leave as-is for standard RF wavelength math.
Build Notes (what these lengths mean)
  • ¼-wave is commonly used for a vertical radiator (often with a ground plane / counterpoise).
  • ½-wave is the total electrical length of a half-wave element. For a simple dipole, each side is ~¼-wave.
  • 5/8-wave is often used for vertical designs where radiation angle and matching matter; tuning is important.
  • These are starting lengths. Nearby metal, height, conductor diameter, insulation, and matching networks change the final cut.

Reference

  • Wavelength: λ = c / f
  • Length: L = λ × fraction × factor
  • Fractions: ¼λ, ½λ, 5/8λ, 1λ

This calculator is intentionally lightweight and deterministic. Use it to get a starting cut length quickly, then trim/tune to your setup.

FAQ

Why don’t my real measurements match exactly?

Real antennas are affected by conductor diameter, insulation, nearby objects, height above ground, and the feed/matching network. This tool gives a clean starting point.

What shortening factor should I use?

If you’re unsure, start with 1.0 (free-space) or try 0.95 as a rough “end-effect” starting estimate. Final tuning still matters.

For a dipole, is ½-wave the whole antenna?

Yes — a simple half-wave dipole is roughly ½-wave total, which is about ¼-wave per side (two legs).

Does this tool compute SWR or matching?

Not here. This tool focuses on lengths. Matching/SWR depends on feed method, ground/counterpoise, and environment.

Tool Info

Last updated:

Updates may include more presets, additional output formats, and better edge-case handling.