Half-Wave Dipole Antenna Length Calculator
Enter the operating frequency in MHz to size a half-wave wire dipole. The tool returns the total wire length and each leg in both feet and metres using the classic 468 formula.
How to use the dipole antenna calculator
- Enter your operating frequency in megahertz, for example 7.15 for the 40 metre band.
- Read the total length and each leg in feet and metres.
- Cut each leg a little long, then trim while checking SWR to fine tune.
Examples
40 metre dipole at 7.15 MHz
frequencyMhz = 7.15
total = 65.45 ft (19.95 m), each leg = 32.73 ft
20 metre dipole at 14.2 MHz
frequencyMhz = 14.2
total = 32.96 ft, each leg = 16.48 ft
Frequently asked questions
What is the dipole length formula?
The total length of a half-wave dipole in feet is 468 divided by the frequency in MHz. Each of the two legs is 234 divided by the frequency. To get metres, multiply feet by 0.3048.
Why 468 and not 492?
A half wavelength in free space is 492 divided by the frequency in MHz. Real wire shortens the resonant length, so 468 is used instead. That difference bakes in a velocity factor of about 0.95 for common wire.
What is velocity factor and should I change the 468 value?
Velocity factor is how much slower a signal travels along the wire than in free space. The 468 constant already assumes about 0.95. Thin insulated wire near other objects can need a slightly smaller constant, so always cut long and trim.
Why cut each leg longer than the calculator says?
Nearby objects, height above ground and wire type all shift resonance. Starting a few inches long on each leg lets you trim down to the lowest SWR rather than ending up too short.
Does this work for any band?
Yes. The formula is valid across the HF, VHF and UHF range. Just enter the frequency in MHz, such as 28.4 for 10 metres or 146 for the 2 metre band.
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