BER vs SNR

Es/No=k* Eb/No

where k=no. of bits per symbol so for QPSK, k=2 and

Es/No=2* Eb/No

Es/No = C/N * B/fs

where

C/N is the carrier-to-noise ratio = SNR,
B is the channel bandwidth in Hertz,
fs is the symbol rate in Baud or symbols/second