Why does 300 divided by the frequency in MHz give the wavelength?

Because the speed of light is 299.792458 × 10^6 m/s, which rounds to 300 × 10^6. Dividing that by a frequency expressed in millions of hertz cancels the 10^6 on both sides and leaves meters. The rounding overstates the wavelength by 0.07%, roughly 1.4 mm at a 2 m wavelength.

Does wavelength change inside a coaxial cable?

Yes. The dielectric slows the wave to a fraction of c called the velocity factor, roughly 0.66 for solid polyethylene and 0.80–0.87 for foam or air-spaced lines. Wavelength drops in proportion, so a half-wave section of RG-58 is only about two thirds as long as a half wave in air.

Where does 5G sit in the spectrum?

Mostly far below the millimetre waves. The great majority of 5G traffic runs in FR1, the sub-6 GHz range, roughly 600 MHz to 4 GHz. That is UHF up to 3 GHz and the bottom edge of SHF above it, with wavelengths from 50 cm down to 7.5 cm. Millimetre wave is FR2 only, 24.25 to 71 GHz (SHF and EHF), where wavelengths run 12 mm down to 4 mm. FR2 is a capacity layer for stadiums, airports and dense city blocks, served by small cells a few hundred metres apart, and it carries a small share of deployed 5G.

Why are low-band antennas so much bigger?

Because element length scales directly with λ, and λ = c / f scales inversely with frequency. A half-wave dipole is 1.03 m at 145 MHz but 83 m at 1.8 MHz, which is why longwave and shortwave stations use masts, wire spans and loading coils instead of a resonant element.

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Frequency ↔ wavelength calculator

Radio waves travel at the speed of light, so frequency and wavelength are two views of one thing: λ = c / f. At 100 MHz the wavelength is 3.00 m; at 2.4 GHz it is 12.5 cm. This calculator converts either way and gives the half- and quarter-wave lengths antennas are cut from, plus the ITU band.

Convert

Frequency

Wavelength λ

2.998 m

= 9.84 ft

Frequency

100 MHz

= 100 MHz

Half wave λ/2

1.499 m

free-space dipole span, before end-effect shortening

Quarter wave λ/4

74.95 cm

whip over a ground plane

ITU band

VHF

Very high frequency · 30 – 300 MHz

The strip splits the radio spectrum into the eight ITU bands, one decade each, on a logarithmic frequency axis. The green frame marks the band the current frequency falls in, and the vertical line marks the frequency itself. Below it, one full cycle of the drawn wave carries the wavelength that goes with that frequency.

Values are for vacuum, and within 0.03% for air. Inside cables and other dielectrics the wave travels slower and the wavelength is correspondingly shorter.

How it works

01
Start from one constant

In vacuum every radio wave travels at c = 299 792 458 m/s, a defined value rather than a measured one. Air slows it by about 0.03%, far below the tolerance of any antenna, so the vacuum figure is what practical RF work uses.
02
Divide, and remember 300

λ = c / f. Because c is close to 300 × 10⁶ m/s, λ in meters is 300 divided by the frequency in MHz. 300/145 = 2.07 m for the 2 m band, 300/2400 = 0.125 m for Wi-Fi. The shortcut is high by 0.07%, which is nothing next to the effect of a nearby roof.
03
Read off the band and the element length

The ITU names one band per decade, VLF (3–30 kHz) through EHF (30–300 GHz). Antennas are sized in fractions of λ: a half-wave dipole is λ/2 tip to tip, a quarter-wave whip over a ground plane is λ/4. At 145 MHz that is 1.03 m and 0.52 m; at 2.4 GHz, 6.2 cm and 3.1 cm.
04
Remember that cables are slower

Inside coax the wave travels at the cable’s velocity factor — typically 0.66 for solid-polyethylene RG-58, 0.85 for foam dielectrics. The electrical wavelength shrinks by the same ratio, so a quarter-wave matching stub is physically shorter than the free-space number this calculator gives.

Formulas

Wavelength from frequency

λ = cf

λ — wavelength, m
f — frequency, Hz
c — speed of light in vacuum, 299 792 458 m/s (exact)

The engineer’s shortcut

λ (m) ≈ 300f (MHz)

300 — c rounded from 299.792458, in units of 10⁶ m/s
the approximation reads 0.07% high — negligible for antenna work

Worked example

The 2 m amateur band

f = 145 MHz
λ = 299 792 458 / 145 000 000 = 2.07 m
λ/2 = 1.03 m ; λ/4 = 0.52 m
→ a “2 m” antenna is really built around 1.03 m (½λ) or 0.52 m (¼λ) elements

FAQ

Why does 300 divided by the frequency in MHz give the wavelength?: Because the speed of light is 299.792458 × 10⁶ m/s, which rounds to 300 × 10⁶. Dividing that by a frequency expressed in millions of hertz cancels the 10⁶ on both sides and leaves meters. The rounding overstates the wavelength by 0.07%, roughly 1.4 mm at a 2 m wavelength.
Does wavelength change inside a coaxial cable?: Yes. The dielectric slows the wave to a fraction of c called the velocity factor, roughly 0.66 for solid polyethylene and 0.80–0.87 for foam or air-spaced lines. Wavelength drops in proportion, so a half-wave section of RG-58 is only about two thirds as long as a half wave in air.
Where does 5G sit in the spectrum?: Mostly far below the millimetre waves. The great majority of 5G traffic runs in FR1, the sub-6 GHz range, roughly 600 MHz to 4 GHz. That is UHF up to 3 GHz and the bottom edge of SHF above it, with wavelengths from 50 cm down to 7.5 cm. Millimetre wave is FR2 only, 24.25 to 71 GHz (SHF and EHF), where wavelengths run 12 mm down to 4 mm. FR2 is a capacity layer for stadiums, airports and dense city blocks, served by small cells a few hundred metres apart, and it carries a small share of deployed 5G.
Why are low-band antennas so much bigger?: Because element length scales directly with λ, and λ = c / f scales inversely with frequency. A half-wave dipole is 1.03 m at 145 MHz but 83 m at 1.8 MHz, which is why longwave and shortwave stations use masts, wire spans and loading coils instead of a resonant element.

Frequency chosen? See how far it reaches over real terrain — the simulator models any frequency from 30 MHz to 80 GHz, free in your browser.

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Related guides

Plan radio coverage (RF / ITM) — the frequency you pick drives every loss the simulator computes

Sources & further reading

CODATA value: speed of light in vacuum — NIST ↗ — the exact defined value of c
Radio spectrum — Wikipedia ↗ — ITU band nomenclature, VLF through THF
ITU Radio Regulations ↗ — the authoritative frequency allocations

Frequency ↔ wavelength calculator

How it works

Start from one constant

Divide, and remember 300

Read off the band and the element length

Remember that cables are slower

Formulas

Worked example

FAQ

Related guides

Sources & further reading

Related tools

Dipole length calculator

Quarter-wave vertical calculator

Wi-Fi channel to frequency converter

Doppler shift calculator