Caculating baud rate of Ethernet per wire
A 100BASE-TX device transmits on 1 pair (2 wires) and receives on another pair (2 more wires). Because of the 4B5B encoding -- for each 4 data bits, it transmits a series of 5 symbols -- 100BASE-TX has a 125 MHz symbol rate (sometimes called the baud rate) on each pair.
Each symbol carries slightly less than 1 bit of information.

1000BASE-T -- Gigabit Ethernet over Cat5 cable -- has exactly the same 125 MHz symbol rate as 100BASE-TX.
A 1000BASE-T device, among other tricks, transmits a 5-level pulse amplitude modulation symbol on each of the 4 pairs simultaneously.
Each of those 4 symbols, transmitted simultaneously on 4 different wire pairs, carries 2 bits of information, giving a bit rate of 125 MSymbols/sec/pair * 2 bit/symbol * 4 pairs = 1000 Mbit/sec.

The 100 Mbps for 100BASE-TX and the 1000 Mbps for 1000BASE-TX are the maximum theoretical bit rates for those systems.
Packet preambles, Ethernet framing, TCP/IP framing, TCP retries, etc. all eat up some of those bits, so the amount of real data bits transferred will be less.