Antenna Length Calculator

Dipole · Monopole · Ground-plane · Yagi — with velocity factor & band presets

Frequency & Antenna

Frequency

Unit

Quick band presets:

Element Type

Velocity Factor ~0.95 for bare wire; free-space theoretical = 1.0

Result

Pick a frequency (or band preset) and element type, then calculate to see element lengths in mm, cm, inch and feet

Resonant-length estimates. Real antennas shift with wire diameter, height above ground, nearby objects and end effects — always trim and check SWR when tuning. Yagi figures are approximate starting points, not a substitute for antenna-modelling software.

Antenna Length Calculator: Find Dipole, Monopole, Ground-Plane and Yagi Element Lengths

Getting an antenna’s element length right for your target frequency is the starting point for it to resonate properly. This tool covers four common types in one place – half-wave dipole, quarter-wave monopole, ground-plane (with radials) and Yagi (with reflector/director spacing) with an adjustable velocity factor for real wire, not just free-space theory. Ready-made band presets for Ham radio, WiFi, FM and GPS save you from looking up frequencies separately.

How to Use

Enter your target frequency or click a band preset (like “2m Ham,” “WiFi 2.4G,” or “FM 98”) to auto-fill it.
Select the antenna type – Dipole, Monopole, Ground-Plane or Yagi.
Adjust the velocity factor if needed (accounts for real-wire resonance being slightly shorter than free-space wavelength).
Click Calculate to see element length(s) – plus radial length for ground-plane or reflector/director lengths and spacing for Yagi.
Results appear in multiple units (mm, cm, inch, ft) at once.

Key Features

Four antenna types: Half-wave Dipole, Quarter-wave Monopole, Ground-Plane and Yagi
Adjustable velocity factor for real-wire versus free-space wavelength
Ready-made band presets: Ham bands (80m–70cm), FM broadcast, WiFi (2.4/5GHz) and GPS L1
Ground-plane mode calculates radial length (~5% longer than driven element) with radial-count guidance
Yagi mode gives starting-point reflector length, director length and element spacing
Multi-unit output – mm, cm, inches and feet simultaneously
Dipole mode shows total tip-to-tip length and per-leg length for wire cutting
Export as PDF or copy the result.

Formula / Logic Used

Free-Space Wavelength $\lambda = \frac{c}{f}$

Where $c$ ≈ 299,792,458 m/s. This is multiplied by the velocity factor to get the real-wire electrical length, since radio waves travel slightly slower in a physical conductor than in free space.

Element Lengths by Antenna Type

Half-wave Dipole (total): $0.5 \times \lambda_{VF}$ (each leg = $0.25 \times \lambda_{VF}$ )
Quarter-wave Monopole: $0.25 \times \lambda_{VF}$
Ground-Plane Driven Element: $0.25 \times \lambda_{VF}$ , with radials at ~ $1.05\times$ that length (slightly longer radials help pull feed impedance toward 50Ω)
Yagi Driven Element: $0.5 \times \lambda_{VF}$ , Reflector at ~ $1.05\times$ the free-space half-wavelength, Director at ~ $0.95\times$ typical spacing $0.15\lambda$ – $0.25\lambda$

Who Should Use This Tool

Ham radio operators and hobbyists building or adjusting wire dipoles, verticals or Yagi beams. Also useful for diploma and B.Tech ECE students learning antenna theory and resonant length calculations.

Frequently Asked Questions (FAQs)

1. How do I calculate the length of a half-wave dipole antenna?

Divide the speed of light by your target frequency to get wavelength, then take half of that (adjusted by velocity factor for real wire) as the total tip-to-tip length. This tool gives you both the total and per-leg length instantly.

2. What is velocity factor and why does it matter for antenna length?

It accounts for radio waves traveling slightly slower through a physical wire than through free space, so the actual resonant length is a bit shorter than pure free-space wavelength suggests. You can adjust it here to match your wire type.

3. How long should the radials be on a ground-plane antenna?

Radials are typically ~5% longer than the quarter-wave driven element, which helps bring the feed impedance closer to the standard 50Ω most equipment expects. This tool calculates both together, plus radial-count guidance.

4. What’s the difference between a Yagi reflector and director length?

The reflector is made ~5% longer than the driven element to reflect signal forward; the director is made ~5% shorter to help focus signal forward. This tool gives starting-point lengths for both, though fine-tuning with modeling software or field testing is usually needed.

5. Can I use this calculator for WiFi or GPS antenna design?

Yes – it includes presets for WiFi (2.4GHz/5GHz) and GPS L1, in addition to Ham radio and FM frequencies, so you get a starting element length quickly for any of these.

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Antenna Length Calculator: Dipole, Monopole, Yagi and Ground-Plane