Frequency to wavelength converter — radio, light and photon energy

How to use the frequency ↔ wavelength converter

1. Type the number in Value.
2. In Unit, choose a frequency (Hz, kHz, MHz, GHz or THz) or a wavelength (km, m, cm, mm, µm, nm or pm). The label in brackets tells you which kind it is.
3. Leave Refractive index of the medium at 1 for vacuum, or set it for a material, for example about 1.33 for water or about 1.5 for glass.
4. Read the main result, the region of the spectrum, the photon energy and the period. Two tables list the frequency in every frequency unit and the wavelength in every length unit.

What it does and when to use it

Frequency and wavelength are two ways of describing the same wave. Radio engineers usually think in MHz and GHz, antenna builders need the wavelength in metres or centimetres, and optics and lasers are described in nanometres. This tool links them through the speed of light and adds the photon energy, which matters in physics, chemistry and photovoltaics.

Use it to size an antenna, convert a laser’s wavelength to THz, find the energy of a photon of a given colour, or check which ITU radio band a frequency belongs to. For plain frequency unit changes such as rpm or Hz to kHz, use the frequency converter. Light colour in kelvin is handled by the mired converter.

How it works

1. The speed in the medium is v = c ÷ n, with c = 299,792,458 m/s (exact by definition of the metre).
2. Frequency in: λ = v ÷ f. Wavelength in (read as the vacuum wavelength): f = c ÷ λ, and the wavelength in the medium is λ ÷ n.
3. Photon energy E = h × f in joules, and E ÷ e in electronvolts.
4. Period = 1 ÷ f.
5. The region uses ITU radio band names up to 3 THz (ELF, SLF, ULF, VLF, LF, MF, HF, VHF, UHF, SHF, EHF, THF), then infrared, visible (380–700 nm, split into conventional colour bands), ultraviolet, X-ray and gamma ray by vacuum wavelength.

Worked examples

Wi-Fi. 2.4 GHz has a vacuum wavelength of 12.4913524167 cm. The region shows “Radio: UHF”.

Green light. 550 nm is 545.077196364 THz, labelled Visible light (green), with a photon energy of 2.25426 eV.

FM radio. 100 MHz has a wavelength of 2.99792458 m, almost exactly 3 m.

Inside optical fibre. 193.4 THz is 1,550.11612203 nm in vacuum. With a refractive index of 1.468 it becomes 1,055.93741282 nm inside the glass, while the frequency stays the same.

Limits and tips

• Wavelengths are read as vacuum values, as telecom and laser wavelengths are quoted, so a “1550 nm” laser gives the same THz at any index; the index only changes the wavelength shown for the medium.
• Electromagnetic waves only. Sound and water waves travel at their own speeds. For a coaxial cable with a velocity factor, set the index to 1 ÷ VF, so a factor of 0.66 becomes about 1.52.
• Very small results, such as the period of visible light, show in scientific notation.
• To size a quarter-wave antenna, divide the wavelength by 4, then use the length converter for inches.