ELECTRONICS · CALCULATOR

Antenna length calculator

Free antenna length calculator: get wavelength, quarter wave and half wave from frequency and velocity factor. The formula is shown; verify against the NEC.

Written by Chameera Sampath · Not yet reviewed by a licensed electrician. See the methodology.

US (NEC) only · NFPA 70 / NEC — locally adopted editionDefaults are US values. Verify the locally adopted NEC edition and project data.Official reference ↗

Project inputs

Measurements

Frequency

MHz

Velocity factor

Updates as inputs change. Unit changes preserve the same physical values.

THE MATH BEHIND THE ANSWER

Method & assumptions

λ = c / f; Lquarter = λ × VF / 4

Approximate electrical length; final tuning depends on geometry and surroundings.

Results do not check every aspect of an electrical installation. The calculators follow US (NEC) practice only; a regional preset changes defaults such as voltage and units, and no result certifies NEC compliance.

Sources and validation →

Worked example

Frequency: 100 MHz · Velocity factor: 0.95

Wavelength: 9.836 ft · Quarter wave: 2.336 ft · Half wave: 4.672 ft

This example uses the stated inputs; results for the entered values appear above.

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Estimating and invoicing tool

Ampxa is developing an estimating and invoicing application for electrical contractors. The list below receives notice when it opens.