Limit of internet speed over air medium calculation?
It’s limited by the same criteria as any medium: Shannon’s information theorem. Basically, bandwidth * SNR.

More precisely, the Shannon-Hartley Equation:


\$ C = B \; log_2 \left( 1 + \frac{S}{N}\right)  \;\;\;\;\;\;\;\;\;\; \rightarrow (1)\$


Where \$B\$ is bandwidth in Hz, \$\frac{S}{N}\$ is the signal-to-noise ratio.

As a practical example, under the right conditions, 802.11ac can achieve over a Gbit of bandwidth using an 80MHz channel.