Dipole and whip antenna length calculator

Enter the frequency you want to use. You get the length of a half-wave dipole, each leg, and a quarter-wave whip.

1Type your numbersUse the white boxes. Tap an example chip if you want a starting point.
2Read the answerThe green panel updates as you type. You cannot edit it.
3See whyThe steps below show the formula with your numbers filled in.

TRY AN EXAMPLE

YOUR NUMBERS · TYPE IN THE WHITE BOXES

Frequency you will use

MHz

That is the 20 meters band.

THE ANSWER · WORKED OUT FOR YOU

Half-wave dipole, total wire

32.84ft

Each leg of the dipole

16 ft 5 in

Dipole in meters

10.01m

Quarter-wave vertical whip

16 ft 5 in

HOW IT WAS WORKED OUT

Dipole (ft) = 468 ÷ f = 468 ÷ 14.25 = 32.84 ft

Each leg = 32.84 ÷ 2 = 16 ft 5 in

Quarter-wave whip (ft) = 234 ÷ f = 234 ÷ 14.25 = 16.42 ft

468 already includes the roughly 5% shortening real wire antennas show. Cut a little long, then trim.

COMMON DIPOLE LENGTHS

Band	Frequency	Total wire	Each leg
80 meters	3.75 MHz	124 ft 10 in	62 ft 5 in
40 meters	7.15 MHz	65 ft 5 in	32 ft 9 in
20 meters	14.25 MHz	32 ft 10 in	16 ft 5 in
15 meters	21.2 MHz	22 ft 1 in	11 ft 0 in
10 meters	28.4 MHz	16 ft 6 in	8 ft 3 in

What this means

A half-wave dipole is two equal wires fed in the middle. The wire is a little shorter than the real half wavelength because of end effects, which is why the formula uses 468 instead of 492.

A quarter-wave vertical whip is half the length of the full dipole.

Dipole L (ft) = 468 / f (MHz) | 1/4-Wave Whip (ft) = 234 / f (MHz)

ON THE EXAM

Longer antenna, lower frequency. If a question asks how a dipole's length changes with frequency, remember that doubling the frequency halves the length.

36 questions in the official pools involve this topic:

Common questions

Why 468 and not 492?

492 would be the length with no end effect. Real wire antennas behave about 5 percent shorter, so 468 divided by the frequency in MHz gives the cutting length in feet.

Should I cut exactly this length?

Cut a little long and trim while you measure the SWR. Nearby objects, wire type and height all shift the real resonant point.

Does an inverted V use the same length?

Close to it. An inverted V usually ends up slightly longer than the formula, so start long and trim.

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