Dipole Antenna Length Calculator
Calculate half-wave dipole element length from target frequency. Includes quarter-wave, full-wave, and 5/8-wave lengths.
About this calculator
This calculator sizes a half-wave dipole antenna using the classic amateur- radio formula: length in feet = 468 / frequency in MHz. That constant already bakes in a wire velocity factor of about 95% -- wire is not free space, and electromagnetic waves travel slightly slower along a real conductor than at the full speed of light, so a physical dipole must be cut a bit shorter than a true free-space half wavelength to resonate at the target frequency. As frequency rises, wavelength shrinks proportionally, so a 2-meter (146 MHz) dipole is roughly nineteen times shorter than an 80-meter (3.5 MHz) dipole -- across the huge range of frequencies amateur and commercial antennas actually cover, that swing dwarfs anything velocity factor (which only realistically ranges from about 93% to 98% for common wire types) can do to the computed length, even though the formula treats a given percentage change in either input identically.
The calculator also derives quarter-wave (for a ground-plane vertical), full-wave, and 5/8-wave lengths, all as simple multiples of the half-wave figure, and reports wire diameter for common AWG gauges as reference information -- wire gauge affects the antenna's bandwidth and mechanical strength but has no measurable effect on the resonant length itself at HF/VHF wavelengths, which is why this calculator does not adjust length for gauge. Real-world antennas are also affected by height above ground, nearby conductors, and insulation (which lowers the velocity factor below bare wire's ~95%), so treat the computed length as a cutting starting point to be trimmed for best VSWR with an antenna analyzer, not a final, guaranteed-resonant dimension.
Inputs
Results
Half-Wave Dipole (Total)
3.21 ft
≈ 7 smartphones
Each Dipole Leg
1.6 ft
≈ 6 credit cards
How to Use This Calculator
- Enter your target operating frequency (MHz).
- Set the velocity factor (0.95 for bare wire, lower for insulated wire).
- Select wire gauge (AWG) -- thicker wire has slightly lower velocity factor.
- Review the half-wave dipole total length and each leg length in both feet and meters.
- Cut wire to the leg length dimension and adjust with an antenna analyzer for best VSWR.
How the result changes with Target Frequency
| Target Frequency | Half-Wave Dipole (Total) | Each Dipole Leg |
|---|---|---|
| 73 | 6.41 ft | 3.21 ft |
| 110 | 4.25 ft | 2.13 ft |
| 219 | 2.14 ft | 1.07 ft |
| 365 | 1.28 ft | 0.64 ft |
What each input means
- Target Frequency
- Center frequency for the antenna in megahertz
- Velocity Factor
- Wire velocity factor (bare copper wire: ~95%, insulated: ~93%)
- Wire Gauge (AWG)
- American Wire Gauge for antenna elements (10-14 AWG typical)
How this is calculated
Formula
Length (ft) = 468 / f(MHz)Worked example, using the default values
- Identify Input ParametersTarget Frequency = 146, Velocity Factor = 95, Wire Gauge (AWG) = 14 = 3 input(s) provided
- Calculate Half-Wave DipoleHalf-Wave Dipole3.21 = 3.21
- Calculate Each Dipole LegEach Dipole Leg1.6 = 1.6
- Calculate Half-Wave DipoleHalf-Wave Dipole0.98 = 0.98
- Calculate Each Dipole LegEach Dipole Leg0.49 = 0.49
Engine last updated . Checked against 4 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does the formula use 468 instead of the theoretical 492 for a free-space half wave?
A true free-space half wavelength in feet is 492 / frequency in MHz (using the speed of light directly), but a real wire dipole is electrically slightly longer relative to its physical length due to end effects and the wire's velocity factor. The empirically derived 468 constant already folds in a typical ~95% velocity factor for bare copper wire, so cutting to 468/f gets you close to resonance without a separate velocity-factor calculation for standard installations.
Why does wire gauge not change the calculated antenna length?
At HF and VHF wavelengths, the resonant length of a wire dipole is governed almost entirely by its length-to-wavelength ratio, not its diameter -- thicker wire does broaden the antenna's usable bandwidth and adds mechanical strength, but the effect on resonant length is small enough that this calculator's simplified 468/f formula does not adjust for it. Wire diameter is shown here only as reference information for planning your build.
How much shorter does insulated wire need to be than bare wire?
Insulation slows the wave slightly more than bare copper does, lowering the effective velocity factor to roughly 93% instead of about 95% for bare wire. Lowering the velocity factor input in this calculator shortens the computed length proportionally, since the length is directly proportional to velocity factor for a fixed target frequency.
Why is each dipole leg exactly half of the total half-wave length?
A dipole is fed at its center and consists of two symmetric wire elements running away from the feedpoint in opposite directions, together forming the full half-wavelength element. Cutting each leg to exactly half of the total computed half-wave length keeps the antenna balanced and centered on the feedpoint, which is the standard way dipoles are built and fed.
Do I need to cut the wire to the exact calculated length?
Treat the calculated length as a starting point rather than a final dimension -- height above ground, nearby structures, and the true velocity factor of your specific wire all shift the actual resonant frequency somewhat from the idealized formula. Most builders cut the elements slightly long, then trim a little at a time while checking VSWR with an antenna analyzer until resonance lands where they want it.
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