RF Frequency to Wavelength Calculator

Frequency and wavelength are inversely related through the universal wave equation, which applies to all electromagnetic radiation — from radio waves to gamma rays.

The Core Formula:

λ = c / f

Where:

• λ (lambda) = Wavelength in meters (m)
• c = Speed of light in vacuum = 299,792,458 m/s ≈ 3 × 10⁸ m/s
• f = Frequency in Hertz (Hz)

Rearranged:

f = c / λ

Energy of a photon (Planck’s equation):

E = h × f = h × c / λ

Where h (Planck’s constant) = 6.626 × 10⁻³⁴ J·s

Worked Example — FM Radio:

• Station frequency: 98.1 MHz = 98,100,000 Hz
• Wavelength: λ = 299,792,458 / 98,100,000 = 3.056 meters
• A quarter-wave whip for that band is λ/4 = 76 cm, which is why a car aerial is about that long

Note the naming, because it trips people up constantly. A dipole is two elements and is a half-wave antenna. A monopole, the single whip working against a ground plane or a car body, is a quarter-wave. There is no such thing as a quarter-wave dipole.

Electromagnetic Spectrum Reference:

Practical Use, and the 5% nobody mentions

Antenna designers use this formula to set wire lengths to fractions of the target wavelength, but the free-space number is never the number you cut. A half-wave at 2.4 GHz works out at 6.25 cm, and a real dipole for that band comes out closer to 5.9 cm. The wire has thickness, and charge piling up at the open ends makes the current behave as though it is travelling through something slower than vacuum. The usual correction is about 0.95, and the fatter the conductor relative to the wavelength, the more you take off.

Amateur radio operators have carried this around as a shorthand for a century: a half-wave dipole in feet is 468 divided by the frequency in MHz, where the free-space figure would give you 492. That gap is the same 5%.

Cut long, then trim. Watching the standing wave ratio dip as you shorten the wire is the only way to land it, and removing a centimetre is easy where adding one means starting again.