Dipole Antenna Calculator
Free dipole antenna calculator: 468 ÷ f MHz gives half-wave length — a 40 m dipole cuts to 65 ft 5 in. Presets for 160 m–70 cm, inverted-V and loop too.
A half-wave dipole’s total length in feet is 468 divided by frequency in MHz, with each leg cut to 234 ÷ f. Enter a frequency above — or tap a ham band preset from 160 m through 70 cm — and the calculator returns the full length and per-leg cut in feet-and-inches and meters, plus three variants: an inverted-V (about 4% shorter), a quarter-wave vertical (234 ÷ f), and a full-wave loop (1005 ÷ f). The numbers are simple: a 40 m dipole cut for 7.15 MHz runs 65 ft 5 in end to end, 32 ft 9 in per side. Cut your wire 2–5% longer than the calculator shows and trim to resonance — height, wire insulation and end effects always pull a real antenna a few percent off the formula. The sections below show where 468 comes from and exactly how to trim.
How long is a dipole for 40 meters?
65 ft 5 in end to end (19.95 m) cut for 7.15 MHz — that’s 468 ÷ 7.15, with each leg 32 ft 9 in. Cut for your sub-band: 66 ft 10 in at 7.0 MHz for CW, 64 ft 1 in at 7.3 MHz at the top of the phone segment. Add 2–3% before cutting and trim to resonance; insulated wire and low mounting height both pull the resonant point lower.
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Dipole Antenna Calculator
| Band | Freq | Dipole Total (468/f) | Each Leg |
|---|---|---|---|
| 80 m | 3.6 MHz | 130′ 0″ | 65′ 0″ |
| 40 m | 7.1 MHz | 65′ 11″ | 32′ 11.5″ |
| 20 m | 14.2 MHz | 32′ 11.5″ | 16′ 5.7″ |
| 15 m | 21.2 MHz | 22′ 0.9″ | 11′ 0.5″ |
| 10 m | 28.4 MHz | 16′ 5.7″ | 8′ 2.9″ |
| 6 m | 50.1 MHz | 9′ 4.1″ | 4′ 8″ |
| 2 m | 146 MHz | 3′ 2.5″ | 1′ 7.2″ |
Key Information
| Parameter | Details |
|---|---|
| Half-wave dipole formula | 468 ÷ f (MHz) = total feet; 234 ÷ f per leg |
| 40 m dipole at 7.15 MHz | 65 ft 5 in total (19.95 m) |
| Practical vs free-space length | ≈95% of 491.8 ÷ f (K = 0.9516) |
| Feedpoint impedance | ≈73 Ω free space; ~1.5:1 SWR on 50 Ω coax |
Frequently Asked Questions
How long is a dipole for 40 meters?
65 ft 5 in end to end (19.95 m) cut for 7.15 MHz — that’s 468 ÷ 7.15, with each leg 32 ft 9 in. Cut for your sub-band: 66 ft 10 in at 7.0 MHz for CW, 64 ft 1 in at 7.3 MHz at the top of the phone segment. Add 2–3% before cutting and trim to resonance; insulated wire and low mounting height both pull the resonant point lower.
How much shorter should an inverted-V be?
About 4–5% shorter than a flat dipole for the same center frequency, which works out to roughly 449 ÷ f in feet. The calculator above applies 4%: a 40 m inverted-V comes out near 62 ft 10 in total instead of 65 ft 5 in. Keep the apex angle between 90 and 120° and the wire ends at least 8–10 ft off the ground; sharper angles shorten the antenna further and drop the feedpoint impedance.
Do I need a license to use a dipole antenna?
Only to transmit. Receiving with a dipole — shortwave listening — is legal in the US with no license at all. To transmit on the amateur bands you need an FCC license: the Technician exam is 35 questions (26 correct passes), typically a $15 session fee plus a $35 FCC application fee, and it’s valid for 10 years. The HF phone segments where dipoles shine mostly require the General class upgrade.
Are these calculators free to use?
Yes, all calculators on CalcCorp are completely free — no registration, no login, no hidden charges. Results are calculated instantly in your browser and we do not store any of your data.
How accurate are these calculations?
Our calculators use standard financial formulas updated with the latest tax rates, interest rates, and government policies for 2026. Results are accurate for planning purposes but should be verified with a professional for final decisions.
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Last updated: March 2026