What this calculator does
A half-wave dipole is the standard reference antenna in amateur radio: a single wire cut to half a wavelength at the intended frequency, fed in the middle, with the two halves running out to either side. This dipole calculator works out the total wire length and the length of each of the two equal legs, from the operating frequency alone.
The 468/f (feet) and 143/f (metres) figures used here are not the raw speed-of-light wavelength calculation; they are the widely published practical dipole antenna length formulas that build in a small correction, the "end effect", for the way a real wire behaves slightly differently from an idealised wave in free space. That is why they are the numbers actually used for cutting wire, not a plain wavelength formula.
The formula
Divide 468 by the frequency in megahertz for the total length in feet, or divide 143 by the frequency in megahertz for the total length in metres. Each leg of the dipole is exactly half of that total length, since the antenna is fed at its centre.
| Term | Meaning |
|---|---|
| Frequency (f) | The operating frequency the antenna is being cut for, in megahertz. |
| Total length | The full end-to-end length of the dipole wire, both legs combined. |
| Leg length | The length of each of the two equal halves running out from the centre feed point. |
The inputs explained
| Field | What to enter |
|---|---|
| Operating frequency (MHz) | The frequency you want the dipole antenna length calculator to work at, in megahertz. This is usually the middle of the band or channel you plan to use. |
When to use it
Cutting wire for an amateur radio band
Amateur bands are identified by frequency, so entering the target frequency, often the middle of the band, gives the wire length to cut before trimming for a final match on the air.
Comparing dipole length across bands
Lower frequencies need much longer wire: an 80 metre band dipole is many times the length of a 10 metre band one, which matters when checking whether a given antenna will physically fit the available space.
Working from either imperial or metric measurements
This antenna length calculator reports both feet and metres at once, so the figure needed depends only on which measuring tape is at hand.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
What length dipole antenna suits each amateur HF band?
Common HF amateur band frequencies, and the resulting dipole antenna length.
| Frequency | Total dipole length (feet) | Total dipole length (metres) | Each leg (feet) |
|---|---|---|---|
| 3.5 MHz | 133.71 ft | 40.86 m | 66.86 ft |
| 7 MHz | 66.86 ft | 20.43 m | 33.43 ft |
| 14.2 MHz | 32.96 ft | 10.07 m | 16.48 ft |
| 21 MHz | 22.29 ft | 6.81 m | 11.14 ft |
| 28 MHz | 16.71 ft | 5.11 m | 8.36 ft |
| 50 MHz | 9.36 ft | 2.86 m | 4.68 ft |
What length dipole suits CB, FM broadcast, VHF and UHF frequencies?
A wider spread of frequencies outside the HF amateur bands, from CB radio up to UHF.
| Frequency | Total dipole length (feet) | Total dipole length (metres) | Each leg (metres) |
|---|---|---|---|
| 27 MHz | 17.33 ft | 5.30 m | 2.65 m |
| 100 MHz | 4.68 ft | 1.43 m | 0.72 m |
| 144 MHz | 3.25 ft | 0.99 m | 0.50 m |
| 446 MHz | 1.05 ft | 0.32 m | 0.16 m |
Questions
Why 468 divided by frequency, rather than the plain wavelength formula?
A plain half-wavelength in free space is slightly longer than what a real dipole needs, because a physical wire has capacitance and thickness effects, known as the end effect, that electrically shorten it. The 468/f (feet) and 143/f (metres) formulas are the practical, widely published figures that already account for this, ready for cutting wire.
Should I cut the wire to exactly this length?
Treat it as a starting point and cut slightly long, then trim in small steps while checking the antenna's match, since factors such as wire height, nearby objects and exact wire gauge shift the ideal length a little from the formula figure.
Does this work for any frequency, not just amateur bands?
Yes. The formula only needs a frequency in megahertz, so it applies equally to CB, FM broadcast, VHF or UHF frequencies, not only the amateur radio bands shown in the tables above.
What is the difference between total length and leg length?
A dipole is fed at its centre, so the total length calculated here is split into two equal legs running out from that feed point in opposite directions; each leg is exactly half the total length.
For the underlying wave relationship between frequency, speed and wavelength that this practical formula is built from, see the wavelength calculator.