Frequency / Wavelength Calculator
Convert between frequency and wavelength with optional velocity factor.
How to Use
- Enter frequency. λ = c/f. Use VF < 1 for cable.
- Also shows ¼λ and ½λ for antennas.
Show Work
Formulas
History of Wavelength and the Speed of Light
Albert Michelson's 1879-1883 measurements of the speed of light at Case Western Reserve, accurate to 300 km/s, set the stage for the relationship λ = c/f to become foundational to radio engineering. Heinrich Hertz's 1887-1888 spark-gap experiments produced wavelengths of ~66 cm — the first deliberate generation of electromagnetic waves at what we now call 454 MHz — and confirmed Maxwell's prediction that light is electromagnetic radiation.
In 1983 the SI redefined the meter as "the length of the path traveled by light in vacuum during a time interval of 1/299792458 of a second" — fixing c to exactly 299,792,458 m/s by definition. Before this, the meter was the standard and c was measured; now c is the standard and the meter derives from it. This is why wavelength calculations use c with no uncertainty.
The velocity factor concept matters for transmission lines and antennas: in a dielectric (coax foam, FR4, Teflon), the wave propagates at v = c/√(ε_r) — typically 0.66c for RG-58 coax, 0.82c for RG-62 twin-lead, 0.5c for microstrip on FR4. Antenna designs use v-factor adjusted wavelengths when computing helical or loaded-section dimensions. For free-space antennas, VF = 1.
About This Calculator
Enter a frequency (with optional units like MHz, GHz) and an optional velocity factor (default 1 for free-space radiation; use 0.66 for RG-58 coax, 0.83 for foam-dielectric coax, 0.5 for FR4 microstrip). The tool returns wavelength λ = c·VF/f, the half-wave (λ/2) dipole length, quarter-wave (λ/4) monopole length above a ground plane, and period T = 1/f.
Practical uses: antenna sizing (quarter-wave whip for 2.4 GHz WiFi = 31.2 mm in free air), PCB trace length vs wavelength (traces > λ/20 need transmission-line design), and cable matching (stubs are λ/4 long). For resonant antennas, add ~5% length compensation for end effects, or use NEC/MMANA simulation. Everything runs client-side; no values leave your browser.
About the Frequency / Wavelength Calculator
Use the Frequency / Wavelength Calculator — a free, easy tool for electronics and circuit design. Nothing is uploaded, and you do not need an account. Convert between frequency and wavelength with optional velocity factor.
How it works
Put each value in its box and read the answer as you go. Because it recalculates live, you can play with the inputs to see how each one moves the result — handy for checking your own working or planning ahead. Everything happens on your device, so it is fast and private.
Want the deeper story? The Knowledge Base explains the ideas behind the tools in more detail.
Frequently Asked Questions
Velocity factor?
Ratio of wave speed in medium to c. Coax ~0.66, twin-lead ~0.82.
Why ¼λ?
Common monopole antenna length above a ground plane.
How do I use the Frequency / Wavelength Calculator?
Simply type your numbers and read the result, which refreshes the instant you change something. There is nothing to submit and nothing to wait for.
Do I need to install or sign up for anything?
Not at all — it runs in the browser with nothing to install and no account. After it loads once, it even works without an internet connection.
Is my information private?
Yes. Everything happens in your browser. Nothing you type is sent to a server or saved anywhere.
Common Use Cases
Antenna Sizing
¼λ whip for 2.4 GHz.
PCB Traces
Trace length vs wavelength.
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