Gigahertz to terahertz: crossing from radio into optics
What this conversion does
It divides by a thousand, which is the smallest possible step on the prefix ladder and yet marks the largest change of method anywhere in the spectrum. Below the boundary, signals are carried in conductors and radiated from antennas; above it, they are handled as light with lenses and mirrors. That the arithmetic is a single division by a thousand is almost an anticlimax given what changes across it.
Where the equipment changes
The handover is usually placed around 300 GHz, which is 0.3 THz. Below it, coaxial cable and waveguide still work; above it, losses in metal become severe and hollow metal pipes stop being practical. The same frequency range is therefore described in gigahertz by the engineers who build the last electronic components and in terahertz by the physicists who use the first optical ones.
Gigahertz to terahertz conversion table
Frequencies on both sides of the electronic-optical boundary, showing how a short step in arithmetic corresponds to a large change in technique.
| Gigahertz (GHz) | Terahertz (THz) |
|---|---|
| 1 | 0.001 |
| 2.4 | 0.0024 |
| 2.45 | 0.00245 |
| 5 | 0.005 |
| 5.8 | 0.0058 |
| 24 | 0.024 |
Why the boundary is not sharp
Nothing fundamental happens at any particular frequency; the change is practical rather than physical. Sources, detectors and transmission lines each reach their limit within roughly the same region, and the exact point depends on the material and the application. The result is an overlap of several hundred gigahertz where both approaches are tried, and a literature that mixes the two units for the same measurements.
Divide by a thousand, then check the size
A terahertz value should be a small fraction for anything below the boundary: 300 GHz is 0.3 THz, and 90 GHz is 0.09. An answer above one means the input was already in the terahertz range, and the result is still correct — it is simply a different part of the spectrum.
Frequently asked questions
How do I convert gigahertz to terahertz?
Divide by a thousand. So 300 GHz is 0.3 THz, and 1000 GHz is exactly 1 THz. The conversion is one step on the prefix ladder, the same relationship as megahertz to gigahertz.
How many gigahertz are in a terahertz?
Exactly one thousand. The two units are adjacent rungs of the SI prefix ladder, so the factor between them is a single power of a thousand, with no intermediate unit involved.
Is 0.3 THz the same as 300 GHz?
Yes, identically. The figure 300 GHz appears in radar and radio specifications while 0.3 THz appears in spectroscopy papers describing the same part of the spectrum, which is why both notations are worth recognising.
Why does the method change at this frequency?
Because above a few hundred gigahertz, losses in metal conductors grow large and the dimensions of waveguides shrink to the point where manufacturing becomes difficult, while optical techniques such as lenses and mirrors start to work well. The spectrum does not change; the toolkit does.
Does the converter accept values above one terahertz?
Yes. Inputs in the thousands of gigahertz convert to values above one terahertz without any special handling, and results are shown in exponent form when a decimal would otherwise run to many places.