An inverted V is a dipole with its centre raised and its ends sloping down, like a shallow tent. It needs only one high support instead of two, which is why it is the most common wire antenna for small gardens and portable stations. But the bent shape changes the antenna slightly: an inverted V resonates a little lower than a flat dipole of the same length, so it must be cut a little shorter. This calculator applies that correction from your apex angle, the angle between the two legs at the top.
The formula starts from the flat dipole: total feet equal 468 divided by frequency in megahertz. Then it multiplies by a V factor. At a 90 degree apex, a fairly sharp V, the factor is 0.95, meaning the antenna is cut 5 percent shorter than a flat dipole. At a 180 degree apex, which is a flat dipole, the factor is 1.00 and there is no correction. Between those points the factor rises in a straight line. Most practical inverted Vs use an apex near 90 to 120 degrees, so the correction is usually 3 to 5 percent.
Here is a worked example. At 14.2 megahertz a flat dipole is about 33 feet total. With a 120 degree apex the factor is about 0.967, so the inverted V total is about 31.9 feet, with each leg near 15.9 feet, or about 9.7 metres total. With a sharper 90 degree apex the factor is 0.95, giving about 31.3 feet total. The difference between the two apex angles is small, well under a foot at this frequency, but it is enough to move resonance noticeably, so it is worth including rather than guessing.
The apex angle also shapes the radiation pattern. A flat dipole radiates mainly broadside, in two directions at right angles to the wire, with deep nulls off the ends. As the V sharpens, the pattern fills in and becomes more omnidirectional, which suits an operator who wants signals from all directions. The cost is a slightly lower feed impedance, often near 50 ohms, which actually suits coaxial cable well. That is a happy accident: the most convenient shape is also a good electrical match for common cable.
Height still matters, and the ends need care. The centre should be as high as you can manage, ideally at least a quarter wavelength up, and the ends should stay well above head height, both for safety and because ends near the ground lose energy and shift resonance. The ends carry high voltage when transmitting, so keep them away from places people touch, and away from gutters, fences, and metal roofs. Insulators at the ends are essential, and a little slack for wind movement prevents snapped wire.
Build practice follows the dipole rule: cut long, then trim. Cut each leg a few percent longer than the calculator says, hang the antenna at its final height and angle, and measure with an antenna analyzer. Trim equal small amounts from both legs and remeasure until the lowest standing wave ratio sits on your chosen frequency. If resonance lands far from the target, check the apex angle and the height before cutting further, because a wrong angle or a nearby metal object can shift resonance more than length alone.
Feeding is straightforward. The feed impedance of a typical inverted V sits near 50 ohms, so 50 ohm coaxial cable connects directly, and a balun at the centre keeps current off the cable shield and keeps the pattern clean. For receiving only, the feed details barely matter. For transmitting, always check standing wave ratio before running full power, and never transmit into an antenna you have not measured, since high reflected power can damage a transmitter and waste your signal as heat.
In short, this tool turns frequency and apex angle into a cut length: the flat dipole length from 468 divided by frequency, shortened by a V factor from 0.95 at 90 degrees to 1.00 when flat, with each leg half the total, in feet and metres. Cut long, hang it high with safe ends, trim in small equal steps while measuring, and respect your licence rules. One support, two wires, and a little arithmetic give you a fine all-round antenna.