Frequency ↔ Wavelength converter

Hertz is the reference unit here, and the multiples — kilohertz, megahertz, gigahertz, terahertz — scale up from it the ordinary way. Wavelength units (meter, centimeter, millimeter, micrometer, nanometer, angstrom) and the electronvolt work differently: they describe the same electromagnetic wave from a different angle, so converting into or out of them isn't a simple multiply, it runs through the speed of light, c ≈ 299,792,458 m/s, and for photon energy, through Planck's constant as well. That's also why wavelength units in this table carry a negative-signed conversion factor behind the scenes — a signal to the calculator that the relationship with frequency is reciprocal rather than proportional.

Frequency and wavelength are tied together by c = λf, so converting nanometers to terahertz means dividing the speed of light by the wavelength:

f = c ÷ λ

Visible blue-green light around 500 nm gives f = 299,792,458 ÷ (500 × 10⁻⁹) ≈ 599.58 THz. The same photon's energy works out to roughly 2.48 eV, a number spectroscopists recognize instantly because it falls right in the middle of the visible spectrum's typical 1.6–3.1 eV range. On the radio end, standard FM broadcast sits near 100 MHz, which converts to 299,792,458 ÷ 100,000,000 ≈ 3 meters of wavelength — a figure antenna designers use directly when sizing a quarter-wave whip. Push the frequency up into the microwave range used by home WiFi, 2.4 GHz, and the wavelength shrinks to 299,792,458 ÷ 2,400,000,000 ≈ 0.125 meters (12.5 cm), which is roughly why a WiFi router's internal antenna elements are only a few centimeters long.

This dual frequency/wavelength language runs through an enormous range of fields: radio and wireless engineers spec antennas and channel bandwidth in MHz/GHz because that's what their transmitters are literally tuned to, optical and laser work is almost always described in nanometers because that's the scale optical components like filters, gratings, and fiber cores are manufactured to, spectroscopists switch to electronvolts when talking about how much energy a photon can deposit in a material (relevant for everything from solar cell efficiency to X-ray radiation safety limits), and astronomers routinely convert between the two when comparing a telescope's wavelength coverage — visible, infrared, radio — to the frequency bands their receivers are built to detect. Even microwave oven design touches this category: household microwaves operate at 2.45 GHz for reasons tied directly to how that frequency's roughly 12 cm wavelength interacts with water molecules in food.

The biggest trap in this category is forgetting that the relationship is inverse, not proportional: doubling a frequency halves the corresponding wavelength, so treating this like an ordinary unit conversion (as if a bigger number in one column meant a bigger number in the other) gives exactly backwards results. It's also easy to mix up nanometers with angstroms — the angstrom is ten times smaller than the nanometer and still shows up constantly in crystallography and X-ray diffraction work, where atomic spacings are naturally measured in angstroms rather than nanometers, a holdover from spectroscopy conventions that predate the widespread use of the nanometer as a standard length unit.