What formula does the calculator use for wavelength?

It uses λ = c / f with c = 299,792,458 m/s in vacuum and f in hertz (your MHz entry × 10⁶). Element lengths multiply λ by 1/4, 1/2, or 5/8, then scale by your velocity factor for a shortened physical wire or element versus free space.

What are the 234 and 468 constants?

They are traditional U.S. ham approximations in feet for a quarter-wave piece of thin wire in air with end effect (234/f) and a half-wave dipole overall length (468/f). They are close to ideal physics but not identical to the SI calculation with velocity factor 1.0.

Why is my antenna electrically longer than the cut length?

Diameter, insulation, nearby conductors, and ground proximity lower velocity on the structure, so the physical length for resonance can be shorter than free-space λ/4 while still behaving electrically like a longer radiator—always prune with instruments.

What velocity factor should I use?

Bare #12–#14 copper in air is often modeled around 0.95–1.0 for first cuts. Coaxial-stub matching networks use the manufacturer VF for that cable type. Antennas with traps or loading coils need full modeling or measurement rather than a single VF.

Does this include velocity of propagation in soil radials?

No. Buried radials, counterpoise wires, and tower capacitance change the feed-point impedance and apparent electrical height; the tool only scales ideal free-space wavelength by the scalar you enter.

Can I use this for 2 m or 70 cm FM verticals?

Yes for a first-order mechanical length of the radiating element. Actual repeater antennas add phasing, stacking, and matching networks that the simple λ/4 or 5λ/8 lines do not capture.

What about duplex offsets?

Cut and tune for the frequency where the antenna must present its design impedance—often the transmit pass for a homebrew duplexer is a different mechanical problem than a single-band dipole.

Is this FCC or CE certification?

No. It is educational geometry only. Field strength, SAR, tower registration, and RF exposure limits are separate regulatory topics.

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Drones & RC

Amateur Radio Antenna Length Calculator

Free amateur radio antenna length calculator for HF through microwave order-of-magnitude planning. Enter frequency in megahertz and a velocity factor to see free-space wavelength plus quarter-, half-, and five-eighths-wave physical lengths in meters and feet, alongside the classic 234/f and 468/f approximations used on many ham workbenches.

Last updated: April 17, 2026

SI wavelength from c / f (MHz → Hz)

λ/4, λ/2, and 5λ/8 with adjustable VF

234/f and 468/f foot cross-checks

Need a branded RF or field operations calculator? Get a Quote

Amateur Radio Antenna Length Calculator

Wavelength and λ/4, λ/2, and 5λ/8 physical lengths from frequency in MHz and a velocity factor—plus classic 234/f and 468/f foot approximations

Frequency (MHz)

Enter carrier or design frequency (not offset).

Velocity factor

Bare wire in air ≈0.95–1.0; coax-stub problems differ.

Highlight element

Lengths

Half-wave (λ/2)

10.0283 m

≈ 32.901 ft

λ (free-space wavelength)21.1121 m

λ/4 × VF5.0141 m (16.451 ft)

λ/2 × VF10.0283 m (32.901 ft)

5λ/8 × VF12.5353 m (41.126 ft)

Classic 234 / f (λ/4 ft, empirical)16.479 ft

Classic 468 / f (λ/2 dipole ft, empirical)32.958 ft

RF safety & compliance:

• Obey Part 97 (or your country's rules), band plans, and power limits—this is geometry only.
• Ground planes, loading coils, and nearby objects change effective electrical length.
• Use an antenna analyzer or bridge before transmitting into a new build.

Antenna length calculator features

MHz input

0.05–6000 MHz window

Bands

LF through SHF planning

Velocity factor

0.50–1.00 scalar

Shortening

Wire vs stub builds

Three elements

Quarter, half, five-eighths

Geometry

Meters & feet

Classic ham ft

234/f and 468/f

Empirical

Field rule-of-thumb

Highlight mode

Pick which element to feature

Dipole vs vertical focus

Free-space c

ITU vacuum constant

299,792,458 m/s

SI baseline

Quick example result

14.2 MHz, VF 0.95, half-wave highlighted (defaults):

10.0283 m

≈ 32.901 ft · classic dipole ≈ 32.958 ft (468/f)

How this antenna length calculator works

Radio energy in a uniform medium travels at the phase velocity of that medium. In vacuum, phase velocity equals c, so wavelength is c divided by frequency. Practical wire antennas are shorter than free space for the same electrical length because of conductor diameter, insulation, and coupling to ground; ham builders often fold that into a single velocity factor multiplier on the ideal λ/4, λ/2, or 5λ/8 segment. The 234 and 468 foot shortcuts predate cheap calculators and remain useful cross-checks on the bench.

Core formulas

λ (m) = c / f
L (m) = (λ / n) × VF
n = 4 (λ/4), 2 (λ/2), or 8/5 (5λ/8)

c = 299,792,458 m/s, f in Hz (MHz × 10⁶). Feet values multiply meters by 3.28084.

Sources & references

ARRL Antenna Book and handbook chaptersPractical cuts, ground systems, and tuning workflows
ITU-R recommendations and national frequency allocationsLegal band edges for your license class

Also see our watt hour calculator for portable field-power budgeting alongside antenna work.

Get Custom Calculator for Your Platform

Example: 20 m SSB slice at 14.2 MHz

Planning output

Default highlights full λ/2 × VF; compare to classic 468/f dipole rule.

Inputs:

f: 14.2 MHz
VF: 0.95
Highlight: λ/2

Lengths:

λ/2 × VF: 10.0283 m (32.901 ft)
468 / f: 32.958 ft

A center-fed dipole uses two quarter-wave-ish legs from the feed; an end-fed half-wave is a different feed topology—always model feed impedance separately.

Frequently Asked Questions

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Drones & RC

Amateur Radio Antenna Length Calculator

Last updated: April 17, 2026

SI wavelength from c / f (MHz → Hz)

λ/4, λ/2, and 5λ/8 with adjustable VF

234/f and 468/f foot cross-checks

Need a branded RF or field operations calculator? Get a Quote

Amateur Radio Antenna Length Calculator

Wavelength and λ/4, λ/2, and 5λ/8 physical lengths from frequency in MHz and a velocity factor—plus classic 234/f and 468/f foot approximations

Frequency (MHz)

Enter carrier or design frequency (not offset).

Velocity factor

Bare wire in air ≈0.95–1.0; coax-stub problems differ.

Highlight element

Lengths

Half-wave (λ/2)

10.0283 m

≈ 32.901 ft

λ (free-space wavelength)21.1121 m

λ/4 × VF5.0141 m (16.451 ft)

λ/2 × VF10.0283 m (32.901 ft)

5λ/8 × VF12.5353 m (41.126 ft)

Classic 234 / f (λ/4 ft, empirical)16.479 ft

Classic 468 / f (λ/2 dipole ft, empirical)32.958 ft

RF safety & compliance:

• Obey Part 97 (or your country's rules), band plans, and power limits—this is geometry only.
• Ground planes, loading coils, and nearby objects change effective electrical length.
• Use an antenna analyzer or bridge before transmitting into a new build.

Antenna length calculator features

MHz input

0.05–6000 MHz window

Bands

LF through SHF planning

Velocity factor

0.50–1.00 scalar

Shortening

Wire vs stub builds

Three elements

Quarter, half, five-eighths

Geometry

Meters & feet

Classic ham ft

234/f and 468/f

Empirical

Field rule-of-thumb

Highlight mode

Pick which element to feature

Dipole vs vertical focus

Free-space c

ITU vacuum constant

299,792,458 m/s

SI baseline

Quick example result

14.2 MHz, VF 0.95, half-wave highlighted (defaults):

10.0283 m

≈ 32.901 ft · classic dipole ≈ 32.958 ft (468/f)

How this antenna length calculator works

Core formulas

λ (m) = c / f
L (m) = (λ / n) × VF
n = 4 (λ/4), 2 (λ/2), or 8/5 (5λ/8)

c = 299,792,458 m/s, f in Hz (MHz × 10⁶). Feet values multiply meters by 3.28084.

Sources & references

ARRL Antenna Book and handbook chaptersPractical cuts, ground systems, and tuning workflows
ITU-R recommendations and national frequency allocationsLegal band edges for your license class

Also see our watt hour calculator for portable field-power budgeting alongside antenna work.

Get Custom Calculator for Your Platform

Example: 20 m SSB slice at 14.2 MHz

Planning output

Default highlights full λ/2 × VF; compare to classic 468/f dipole rule.

Inputs:

f: 14.2 MHz
VF: 0.95
Highlight: λ/2

Lengths:

λ/2 × VF: 10.0283 m (32.901 ft)
468 / f: 32.958 ft

A center-fed dipole uses two quarter-wave-ish legs from the feed; an end-fed half-wave is a different feed topology—always model feed impedance separately.