Half-Wave Dipole Length
l = 0.95 × c / (2 × f)
Quick answer
This calculator solves l = 0.95 × c / (2 × f) for Dipole Length. With Frequency 10 MHz, the result is 14.24 m. It solves in 2 directions, so you can enter the values you have and get the one you need.
Calculator
Formula
Description
The half-wave dipole is the fundamental reference antenna in radio engineering, consisting of two quarter-wave elements fed at the center. The 0.95 factor accounts for the velocity factor and end effects that make the physical length slightly shorter than the free-space half wavelength. A half-wave dipole has a theoretical gain of 2.15 dBi and a feedpoint impedance of approximately 73Ω in free space, making it a reasonable match to 50Ω coaxial cable. It is the starting point for most amateur radio antenna projects.
Variables
- l — Total dipole length tip to tip (m)
- f — Resonant frequency (Hz)
Practical Notes
The classic ham radio dipole formula in feet is l = 468/f_MHz, which incorporates the 0.95 velocity factor. Height above ground significantly affects impedance and radiation pattern: at 0.5 wavelength height the pattern is mostly broadside, while lower heights tilt the pattern upward. An inverted-V dipole (apex up, ends drooping at 90-120°) is a practical compromise for limited space with only a slight reduction in performance.
Symbols and units
| Symbol | Meaning | Default unit | Accepted units |
|---|---|---|---|
| l | Dipole Length | m | mm, cm, m, km |
| f | Frequency | MHz | Hz, kHz, MHz, GHz |
Step by step
- 1. What you know: Frequency 10 MHz
- 2. The relation: l = 0.95 × c / (2 × f)
- 3. Substitute: f = 10 MHz
- 4. Result: Dipole Length = 14.24 m
Worked examples
Minimum range
Given: Frequency 100 kHz
Result: Dipole Length = 1.424 km
Low range
Given: Frequency 1 MHz
Result: Dipole Length = 142.4 m
Typical
Given: Frequency 10 MHz
Result: Dipole Length = 14.24 m
High range
Given: Frequency 100 MHz
Result: Dipole Length = 1.424 m
Maximum range
Given: Frequency 1 GHz
Result: Dipole Length = 14.24 cm
Solving for each variable
Solve for Dipole Length
Frequency 100 kHz → 1.424 km
Solve for Frequency
Dipole Length 1 mm → 142.4 GHz
How Dipole Length changes with Frequency
| Frequency (input) | Dipole Length (result) |
|---|---|
| 1 MHz | 142.4 m |
| 2.5 MHz | 56.96 m |
| 5 MHz | 28.48 m |
| 7.5 MHz | 18.99 m |
| 10 MHz | 14.24 m |
| 15 MHz | 9.493 m |
| 20 MHz | 7.12 m |
| 40 MHz | 3.56 m |
| 70 MHz | 2.034 m |
| 100 MHz | 1.424 m |
The same result in other units
| Unit | Value |
|---|---|
| mm | 14240 |
| cm | 1424 |
| m | 14.24 |
| km | 0.01424 |
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<p><a href="https://vbatpower.com/formulas/half-wave-dipole/">Half-Wave Dipole Length</a> Calculator by vbatpower.com</p>Frequently asked questions
How do you calculate Half-Wave Dipole Length?
Use l = 0.95 × c / (2 × f). With Frequency 10 MHz, Dipole Length works out to 14.24 m.
What is the formula for Half-Wave Dipole Length?
The formula is l = 0.95 × c / (2 × f). The half-wave dipole is the fundamental reference antenna in radio engineering, consisting of two quarter-wave elements fed at the center.
How do you find Frequency when you know the other values?
Rearrange for Frequency: with Dipole Length 1 mm, Frequency is 142.4 GHz.
What units does Half-Wave Dipole Length use?
Dipole Length is shown in mm, cm, m, km. Values are held in SI base units internally, so you can mix prefixes without converting by hand.
Related Concepts
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