The MIB in LTE tell the UE the prevalent Channel Bandwith in number of resource blocks
value of dl-bandwidth as in MIB corresponds to :
6 = 1.4 MHz
15 = 3 MHz
25 = 5 MHz
50 = 10 MHz
75 = 15MHz
100 = 20 MHz
Definition of channel bandwidth and transmission bandwidth configuration for one E‑UTRA carrier
source 3GPP TS 36.101