BTS erlang capacity depends on two factor:
1-GOS that is grade of service
2- no. of trx’s
say a sector(bts) comprises of 3 trx’s one trx is as BCCH.
NOW ACCORDING TO GOS=2% and Erlang B table -one trx means 8 channels as good as 8 trunks the erlang capacity is 3.63erlangs. now for BCCH TRX -2channels are used for signalling on Air intrface remaining is 6 channels now as per GOS=2% AND ERLANG b TABLE the traffic carrying capacity is 2.27erlangs.so two trx’s with 8 channels and 1 with 6 channels gives you the total erlang capacity of whol sector as 2.27+3.63+3.63=9.53erlangs……..
I think that may clear your doubts