For classful networks, the available addresses are given by the [Wikipedia page on Classful Networks](https://en.wikipedia.org/wiki/Classful_network). 

Class A = 16,777,214

Class B = 65534

Class C = 254 

The Wikipedia page also discusses the calculation:

> The number of addresses usable for addressing specific hosts in each network is always 2<sup>N</sup> - 2, where N is the number of rest field bits, and the subtraction of 2 adjusts for the use of the all-bits-zero host portion for network address and the all-bits-one host portion as a broadcast address. Thus, for a Class C address with 8 bits available in the host field, the number of hosts is 254.

It's worth noting that nobody uses classful networks anymore.