Max erlang capacity for a cell depends on the carrier. For eg. one carrier has 7TCH and at a 0.1% GOS the Erlangs will be 2.9 for 2TRX with same GOS we will have 8.2Erlang. and so on.
Erlang u can get beased on the no of TCH available on air interface and Abis interface, depending on the GOS. U can use the Erlang table