Dipole Antenna Frequency Calculator

Choose a mode, enter values, then calculate. The form uses a responsive grid: three columns on large screens, two on smaller, and one on mobile.

Calculation mode Frequency from total length Total length from frequency

Switch anytime; inputs toggle automatically.

Total dipole length

m cm mm ft in

Tip-to-tip length for a center-fed dipole.

Target frequency

Hz kHz MHz GHz

Common HF values are usually in MHz.

Velocity factor (VF)

Bare wire is near 1.0. Insulated wire is lower.

End-effect factor

Typical dipoles use 0.93–0.98 depending on diameter.

Odd harmonic (n)

Use 1 for fundamental. Use 3 or 5 for harmonics.

Trim allowance (%)

Adds extra wire for trimming during tuning.

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Formula used

A center-fed dipole resonates near an odd multiple of a half wavelength. This calculator uses a speed-of-light model with practical correction factors.

The optional 468 rule shown in results is a common approximation in feet and MHz.

How to use this calculator

1. Select the calculation mode you need.
2. Enter either total dipole length or target frequency.
3. Set velocity factor for your wire insulation.
4. Set end-effect for wire diameter and nearby objects.
5. Choose harmonic 1 for fundamental or 3 for tuning higher.
6. Press Calculate to view results above the form.
7. Use CSV or PDF buttons to save the results.

Dipole antenna frequency guide

1) What “resonant” means for a dipole

A center‑fed dipole is closest to resonance when its total length is about half a wavelength. At resonance, feedpoint reactance is near zero and power transfer improves. Real dipoles are shortened by conductor diameter, nearby objects, and insulation.

2) Typical bands and practical lengths

HF dipoles are often sized for 3.5, 7.1, 14.2, 21.2, or 28.5 MHz. For example, a 7.1 MHz half‑wave dipole is roughly 20 m long. A 14.2 MHz dipole is about half that length.

3) Why velocity factor changes results

Velocity factor models how waves travel along a conductor in real conditions. Bare wire is near 1.00, while insulated wire is commonly 0.90–0.98. Lower VF means a slightly shorter physical dipole for the same frequency.

4) End‑effect factor and wire diameter

The electric field fringing at the ends makes dipoles behave “electrically longer.” Thicker conductors and larger end caps increase this effect. Many builders use 0.93–0.98 as a starting factor, then fine‑tune by trimming.

5) Using odd harmonics for multi‑band work

A half‑wave dipole can also resonate at odd harmonics: 3rd, 5th, and higher. A dipole cut for 7 MHz may show a usable resonance near 21 MHz. Harmonic performance depends on feedline, height, and matching.

6) Trim allowance and tuning workflow

Start slightly long, then trim equally from both legs. This tool’s trim allowance suggests an initial cut length for adjustments. Measure SWR near the target frequency and shorten in small steps. Stop when the minimum SWR aligns with your operating center.

7) Height above ground and nearby objects

Height changes radiation angle and can shift resonance modestly. Trees, gutters, metal railings, and wet roofs can detune the antenna. Keep the dipole clear of large conductive surfaces when possible. Recheck tuning after permanent installation.

8) Reading the outputs for better builds

The calculator shows wavelength, half‑wave, and quarter‑wave references in meters. It also provides each‑leg length, plus a suggested cut length for trimming. Export results as CSV for logging builds, or PDF for sharing a design sheet.